Preservation of organic carbon in the ocean floor

On geological timescales, the burial rate of sedimentary organic carbon exerts major control on the concentrations of atmospheric oxygen and carbon dioxide and thus substantially influences Earth's environmental conditions. In marine sediments, about 20 percent of the organic carbon is directly bound to reactive iron oxides (FeR). However, the fate of reactive iron-bound organic carbon (FeR-OC) in subseafloor sediments and its availability to microorganisms, remain undetermined.

To study this, the team reconstructed continuous FeR-OC records in two sediment cores of the northern South China Sea encompassing the suboxic to methanic biogeochemical zones and reaching a maximum age of around 100,000 years.

The study reveals that in sulfate-methane transition zone (SMTZ) with high microbial activities, FeR-OC is remobilized during microbial-mediated iron reduction processes, and consequently remineralized by microorganisms.

The energy produced is able to support a substantial fraction of microbial life in the SMTZ, which is around one meter thick.

With the exception of the SMTZ, a relatively stable proportion of the total organic carbon survives the microbial degradation processes as FeR-OC and is stored in marine sediments over geological time periods.

"This means," says Dr. Yunru Chen, first author of the study and now a postdoctoral researcher at the Cluster of Excellence 'The Ocean Floor -- Uncharted Interface of the Earth, "that the estimated global reservoir of FeR-OC in microbially active Quaternary marine sediments could be 18 to 45 times larger than the atmospheric carbon pool."

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Ocean floor a 'reservoir' of plastic pollution

New research from CSIRO, Australia's national science agency, and the University of Toronto in Canada, estimates up to 11 million tonnes of plastic pollution is sitting on the ocean floor.

Every minute, a garbage truck's worth of plastic enters the ocean.

With plastic use expected to double by 2040, understanding how and where it travels is crucial to protecting marine ecosystems and wildlife.

Dr Denise Hardesty, Senior Research Scientist with CSIRO, said this is the first estimate of how much plastic waste ends up on the ocean floor, where it accumulates before being broken down into smaller pieces and mixed into ocean sediment.

"We know that millions of tonnes of plastic waste enter our oceans every year but what we didn't know is how much of this pollution ends up on our ocean floor," Dr Hardesty said.

"We discovered that the ocean floor has become a resting place, or reservoir, for most plastic pollution, with between 3 to 11 million tonnes of plastic estimated to be sinking to the ocean floor.

"While there has been a previous estimate of microplastics on the seafloor, this research looks at larger items, from nets and cups to plastic bags and everything in between."

Ms Alice Zhu, a PhD Candidate from the University of Toronto who led the study, said the estimate of plastic pollution on the ocean floor could be up to 100 times more than the amount of plastic floating on the ocean's surface based on recent estimates.

"The ocean surface is a temporary resting place of plastic so it is expected that if we can stop plastic entering our oceans, the amount would be reduced," Ms Zhu said.

"However, our research found that plastic will continue to end up in the deep ocean, which becomes a permanent resting place or sink for marine plastic pollution,"

Scientific data was used to build two predictive models to estimate the amount and distribution of plastic on the ocean floor -- one based on data from remote operated vehicles (ROVs) and the other from bottom trawls.

Using ROV data, 3 to 11 million metric tonnes of plastic pollution is estimated to reside on the ocean floor.

The ROV results also reveal that plastic mass clusters around continents -- approximately half (46 per cent) of the predicted plastic mass on the global ocean floor resides above 200 m depth.

The ocean depths, from 200 m to as deep as 11,000 m contains the remainder of predicted plastic mass (54 per cent).

Although inland and coastal seas cover much less surface area than oceans (11 per cent vs 56 per cent out of the entire Earth's area), these areas are predicted to hold as much plastic mass as does the rest of the ocean floor.

"These findings help to fill a longstanding knowledge gap on the behaviour of plastic in the marine environment," Ms Zhu said.

"Understanding the driving forces behind the transport and accumulation of plastic in the deep ocean will help to inform source reduction and environmental remediation efforts, thereby reducing the risks that plastic pollution may pose to marine life."

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Apex predator of the Cambrian likely sought soft over crunchy prey

Biomechanical studies on the arachnid-like front “legs” of an extinct apex predator show that the 2-foot (60-centimeter) marine animal Anomalocaris canadensis was likely much weaker than once assumed. One of the largest animals to live during the Cambrian, it was probably agile and fast, darting after soft prey in the open water rather than pursuing hard-shelled creatures on the ocean floor. The study is published today in the journal Proceedings of the Royal Society B.

First discovered in the late 1800s, Anomalocaris canadensis—which means “weird shrimp from Canada” in Latin—has long been thought to be responsible for some of the scarred and crushed trilobite exoskeletons paleontologists have found in the fossil record.

“That didn’t sit right with me, because trilobites have a very strong exoskeleton, which they essentially make out of rock, while this animal would have mostly been soft and squishy,” said lead author Russell Bicknell, a postdoctoral researcher in the American Museum of Natural History’s Division of Paleontology, who conducted the work while at the University of New England in Australia.

Recent research on the armor-plated, ring-shaped mouthparts of A. canadensis lays doubt on the animal’s ability to process hard food. The latest study set out to investigate whether the predator’s long, spiny front appendages could do the job instead.

The first step for the research team, which included scientists from Germany, China, Switzerland, the United Kingdom, and Australia, was to build a 3D reconstruction of A. canadensis from the extraordinarily well-preserved—but flattened—fossils of the animal that have been found in Canada’s 508-million-year-old Burgess Shale. Using modern whip scorpions and whip spiders as analogues, the team was able to show that the predator’s segmented appendages were able to grab prey and could both stretch out and flex.

A modeling technique called finite element analysis was used to show the stress and strain points on this grasping behavior of A. canadensis, illustrating that its appendages would have been damaged while grabbing hard prey like trilobites. The researchers used computational fluid dynamics to place the 3D model of the predator in a virtual current to predict what body position it would likely use while swimming.

The combination of these biomechanical modeling techniques—used together in a scientific paper for the first time—paint a different picture of A. canadensis than was previously assumed. The animal was likely a speedy swimmer, zooming after soft prey in the water column with its front appendages outstretched.

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