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Building Blocks
Based on 'Hot Zone' blog entries for astrobio.net
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Climate
Posted:   04/04/10
Author:    Alison Hawkes

Summary: Astrobiology Magazine's climate blog, the Hot Zone, discusses the ways in which life can impact the physical conditions of the Earth. A recent study shows that the health of a single microbial species in the Earth's oceans could eventually alter the ocean food chain - and possibly the Earth's biosphere as a whole.


It’s common to think of physical conditions as the building blocks of life. A plant’s growth is limited by the amount of light, rainfall, and the type of soil. Changing climate conditions these days – drought, warmer weather, sea level rise — is typically seen as a primary driver of a species’ ability to adapt or die.

But it’s important to remember that life can also drastically impact the basic physical conditions of the Earth’s systems. Oxygen in the atmosphere is the result of plant photosynthesis, making the Earth habitable for the entire animal kingdom. And some interesting research is showing that the reflectivity of clouds — which radiates sunlight back into space, thereby serving as a planetary cooling system — is influenced by the metabolic process of tiny marine bacteria.

At the Society for Microbiology’s spring meeting in Edinburgh, Newcastle University postgraduate researcher Michael Maguire gained a lot of attention for his experiments simulating ocean acidification. The greater the acidity, the greater the die-off in an important type of bacteria known as the Marine Roseobacter clade.

This “clade,” a major branch of the Tree of Life, has a widespread distribution, inhabiting areas as diverse as deep sea sediments to coastal waters and the Poles. It represents some 25 percent of the total bacteria community. So it shouldn’t be surprising then that its metabolic activities can scale up to a huge impact.

The Marine Roseobacter breaks down a sulphur compound, dimethylsulfoniopropionate (DMSP) that’s produced by photosynthesizing phytoplankton. Much of that end product is used by other bacteria as a source of sulphur or breaks down further into dimethylsulfide (DMS), incidentally the chemical compound that’s responsible for the smell of the seaside.

When oxidized into the atmosphere, DMS turns into sulphur aerosol particles that make clouds reflect sunlight.

It’s a complicated process, but some have hypothesized that this system operates as a major feedback loop between the oceans and the Earth’s climate. So what happens when the metabolizing Marine Roseobacter can’t withstand the lower pH of ocean water?

How will the ocean food chain survive without the availability of sulphur? And will less sulphur in the air result in a drop in atmospheric reflectivity, thereby warming the climate further? The feedback of biological and physical processes flattens when just one building block falls down.


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