Life under pressure. I’m not talking about the present state of my academic life, although I am starting to feel the squeeze. In this instance it’s not the weight of a PhD bearing down, it’s the weight of 11 kms of water, or 1100 atmospheres to be precise. Research recently published in Nature Geoscience describes the latest findings from Challenger Deep, the deepest part of the Mariana Trench (not to be confused with the Deep-sea Challenger which was the submarine that took James Cameron in to Challenger Deep). For those who didn’t read Claire’s previous post, the Mariana Trench is the deepest point on Earth, a vast chasm that stretches 11km down in to the abyss. It is hard to believe that life can exist under such extreme conditions, but this new research shows that life has not only adapted to survive, it is thriving under immense pressure, near freezing temperatures and absolute darkness. Sounds delightful.
It has long been a problem of the deep-sea researcher, that any samples removed from the deep suffer barotrauma when taken from their natural surroundings. To circumvent the extreme pressure gradient between the surface and the very deep, researchers sent down autonomous samplers so that they could make their measurements in situ (see inset). And once again bacteria living in extreme environments make the headlines. First it was extremophiles from the Antarctic, then below the Antarctic, and now the deepest place on Earth.
Glud and colleauges report that oxygen consumption at Challenger Deep was far greater than the reference site (a shallow 6km), and that sedimentary bacterial counts indicate a surprisingly active microbial community. I’m sure the first question that springs to mind is, ‘but what on earth are they feeding on?’ And that’s an excellent question. Currently our best estimates are that as little as 1-2% of surface derived organic matter actually reaches the depths of the average seafloor, which is around 4 km. The breakdown and reprocessing that occurs to organic matter beyond this distance is largely unknown, but this recent study found that more rather than less organic carbon could be found at the deeper of the two sites. The ratio of lead to radium isotopes was used as a proxy for sediment deposition and particle scavenging, with the researchers concluding that organic matter is being funnelled in to the trench, a process known as sediment focussing. But beyond its importance for sustaining deep sea ecosystems this discovery also improves our understanding of the carbon cycle.
When James Cameron was asked about his mission in to the abyss he described it as a “sterile, almost desert-like place”, but what he couldn’t possibly have seen was that the desert is teeming with life.