While the world wrangles over ways of reducing carbon emissions, some scientists are considering more radical approaches to mitigating the effects of climate change. Dumping iron dust into the world’s oceans is one such strategy. Theoretically, the iron should act as fertiliser, providing a key nutrient that will spur the growth of photosynthetic plankton. These creatures act as carbon dioxide pumps, removing the problematic gas from the air and storing the carbon within their own tissues. When the plankton die, they sink, trapping their carbon in the abyss for thousands of years.
It may seem like a fanciful idea, but as with much of our technology, nature beat us to it long ago. Trish Lavery from Flinders University has found that sperm whales fertilise the Southern Ocean in exactly this way, using their own faeces. Their dung is loaded with iron and it stimulates the growth of plankton just as well as iron dust does.
Sperm whales are prodigious divers, descending to great depths in search of prey like squid. When they’re deeply submerged, they shut down all their non-essential bodily functions. Excretion is one of these and the whales only ever defecate when they reach the surface. By happy coincidence, that’s where photosynthetic plankton (phytoplankton) make their home – in the shallow column of water where sunlight still penetrates. So by eating iron-rich prey at great depths and expelling the remains in the shallows, the whales act as giant farmers, unwittingly seeding the surface waters with fertiliser.
There are approximately 12,000 sperm whales left in the Southern Ocean. By modelling the amount of food they eat, the iron content of that food, and how much iron they expel in their faeces, Lavery calculated that these whales excrete around 50 tonnes of iron into the ocean every year. And based on the results of our own iron fertilisation experiments, the duo calculated that every year, this amount of iron traps over 400,000 tonnes of carbon in the depths, within the bodies of sinking plankton.
Previously, scientists assumed that whales (and their carbon dioxide-rich exhalations) would actually weaken the Southern Ocean’s ability to act as a CO2 pump. But according to Lavery, this isn’t true. She worked out that the whales pump out just 160,000 tonnes of carbon through their various orifices. All of these figures are probably conservative underestimates but even so, they suggest that sperm whales remove around 240,000 more tonnes of carbon from the atmosphere than they add back in. They are giant, blubbery carbon sinks.
However, their true potential will go largely unfulfilled thanks to our harpoons. Many sperm whales have been killed by industrial whalers, and the population in the Southern Ocean has declined by some 90%. On the bright side, the Southern Ocean’s population represent just 3% of the global total, so this species may have an even greater role as a warden for carbon than Lavery has suggested. Other seagoing mammals probably have a part to play too, provided that they feed at depth and excrete near the surface. Several other toothed whales do this, and some filter-feeding ones may do too.
Reference: Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2010.0863
Image by Cianc
The Not Exactly Pocket Science experiment continues after the vast majority of people who commented liked the pilot post. I’m really enjoying this, for quite unexpected reasons. It’s forcing me to flex writing muscles that usually don’t get much of a workout. Writing short pieces means being far more economical with language and detail than usual. It means packing in as much information as possible while still keeping things readable. And it means blitz-reading papers and writing quickly without losing any accuracy.
One quick note before the good stuff: last time, a few people suggested that I put each NEPS item in a separate post, but the majority preferred multiple items per post. For now, I’m keeping it that way because otherwise, the longer pieces would be diluted by the smaller ones. We’ll see how that works for the foreseeable future.
Rising DAMPs – when enslaved bacteria turn our bodies against themselves
Our immune systems provide excellent defence against marauding hordes of bacteria, viruses and parasites, using sentinel proteins to detect the telltale molecules of intruders. But these defences can be our downfall if they recognise our own bodies as enemies.
All of our cells contain small energy-supplying structures called mitochondria. They’re descendents of ancient bacteria that were engulfed and domesticated by our ancestor cells. They’ve come a long way but they still retain enough of a bacterial flavour to confuse our immune system, should they break free of their cellular homes. An injury, for example, can set them free. If cells shatter, fragments of mitochondria are released into the bloodstream including their own DNA and amino acids that are typical of bacteria. Qin Zhang showed that trauma patients have far higher levels of such molecules in their blood than unharmed people. Our white blood cells have sentinel proteins that latch onto these molecules and their presence (incorrectly) says that a bacterial invasion is underway.
This discovery solves a medical mystery. People who suffer from severe injuries sometimes undergo a dramatic and potentially fatal reaction called “systemic inflammatory response syndrome” or SIRS, where inflammation courses through the whole body and organs start shutting down. This looks a lot like sepsis, an equally dramatic response to an infection. However, crushing injuries and burns can cause SIRS without any accompanying infections. Now we know why – SIRS is caused by the freed fragments of former bacteria setting off a false alarm in the body. The technical term for these enemies within is “damage-associated molecular patterns” or DAMPs.
More from Heidi Ledford at Nature News
Reference: Nature DOI:10.1038/nature08780
Different gut bacteria lead to mice to overeat
On Wednesday, I wrote about the hidden legions residing up your bum – bacteria and other microbes, living in their millions and outnumbering your cells by ten to one. These communities wield a big influence over our health, depending on who their members are. Matam Vijay-Kumar found that different species colonise the guts of mice with weakened immune systems, and this shifted membership is linked to metabolic syndrome, a group of obesity-related symptoms that increase the risk of heart disease and type 2 diabetes.
Vijay-Kumar’s mice lacked the vital immune gene TLR5, which defends the gut against infections. Their bowels had 116 species of bacteria that were either far more or less common than usual. They also overate, became fat, developed high blood pressure and became resistant to insulin – classic signs of metabolic syndrome. When Vijay-Kumar transplanted the gut menagerie from the mutant mice to normal ones, whose own bacteria had been massacred with antibiotics, the recipients also developed signs of metabolic syndrome. It was clear evidence that the bacteria were causing the symptoms and not the other way round.
Vijay-Kumar thinks that without the influence of TLR5, the mice don’t know what to make of their unusual gut residents. They react by releasing chemicals that trigger a mild but persistent inflammation. These same signals encourage the mice to eat more, and they make local cells resistant to the effects of insulin. Other aspects of the metabolic syndrome soon follow. The details still need to be confirmed but for now, studies like this show us how foolish it is to regard obesity as a simple matter of failing willpower. It might all come down to overeating and inactivity, but there are many subtle reasons why an individual might eat too much. The microscopic community within our guts are one of them.
Reference: Science DOI:10.1126/science.1179721
The stretchy iron-clad beards of mussels
For humans, beards are for catching food, looking like a druid, and getting tenure. But other animals have beards with far more practical purposes – mussels literally have beards of iron that they use as anchors. The beard, or byssus, is a collection of 50-100 sticky threads. Each is no thicker than a human hair but they’re so good at fastening the mussels to wave-swept rocks that scientists are using them as the inspiration for glue. So they should. The byssus is a marvel of bioengineering – hard enough to hold the mussel in place, but also stretchy enough so that they can extend without breaking.
The mussel secretes each thread with its foot, first laying down a protein-based core and then covering it in a thick protective layer that’s much harder. When Matthew Harrington looked at the strands under a microscope, he saw that the outer layer is a composite structure of tiny granules amid a looser matrix. The granules consist of iron and a protein called mfp-1, heavily linked to one other – this makes the byssus hard. The matrix is a looser collection of the same material, where mfp-is 1 heavily coiled but easy to straighten – this lets the byssus stretch. The granules have a bit of give to them but at higher strains, they hold firm while the matrix continues extending. If cracks start to form, the granules stop them from spreading.
It’s unclear how the mussel creates such a complicated pattern, but Harrington suggests that it could be deceptively simple – changing a single amino acid in the mfp-1 protein allows it to cross-link more heavily with iron. That’s the difference between the tighter granular bundles, and the looser ones they sit among.
Reference: Science DOI:10.1126/science.1181044
Cause of dinosaur extinction
Sixty-five million years ago, the vast majority of dinosaurs were wiped out. Now, a new paper reveals the true cause of their demise – legions of zombies armed with chaingu… wait… oh. Right. An asteroid. You knew that.
More from Mark Henderson at the Times
Reference: Science DOI:10.1126/science.1177265
Say the word iceberg, and most people are likely to free-associate it with ‘Titanic’. Thanks to James Cameron (and, well, history too), the iceberg now has a reputation as an cold murderous force of nature, sinking both ships and Leonardo DiCaprio. But a new study shows that icebergs are not harbingers of death but hotspots of life.
In the late 1980s, about 200,000 icebergs roamed across the Southern Ocean. They range in size from puny ‘growlers’, less than a metre long, to massive blocks of ice, larger than some small countries.
They may be inert frozen lumps, but icebergs are secretly in the business of nutrient-trafficking. As the ice around Antarctica melts in the face of global warming, some parts break free from the parent continent and strike out on their own. As they melt, they release stored minerals into the water around them, and these turn them into mobile homes for a variety of life.
Kenneth L. Smith Jr, from the Monterey Bay Aquarium Research Institute, and other scientists from San Diego discovered the true extent of these icy ecosystems by studying two icebergs floating in the Antarctic Weddell Sea. Even the smaller of the two, W-86, has a surface area larger than 17 football pitches. The larger one, A-52 was over a thousand times bigger, with a surface area of 300 km2 and extending 230 metres into the freezing waters.
Smith and crew identified the duo through satellite imaging, and tracked them down by boat. Their ship spiralled around the blocks of ice collecting water samples as it went, from a dangerously close distance of a few hundred feet to a safer five miles away.
Antarctica normally conjures images of white and blue, but the frozen continent can sometimes bear more unexpected colours. Take the Taylor Glacier – when geologist Griffith Taylor first explored it a century ago, he found a bizarre reddish stain that seemed to spill waterfall-like from the glacier’s snout. The area became evocatively known as Blood Falls.
The source of the blood-red colour is an underground saltwater lake that was trapped by the encroaching glacier at least 1.5 million years ago. The temperature of the water is -5 Celsius, but it’s so salty that it doesn’t freeze. It’s also rich in iron salts, which are slowly leaching the ice – these are the source of the distinctive red hue. Blood Falls is a rust glacier.
But it also houses another secret, which scientists from Harvard University have started to uncover – it’s home to an entire ecosystem of bacteria, trapped for millennia in conditions that could hardly be more inhospitable to life.
Neither water from the surface nor light from the sun penetrates the thick ice of Taylor Glacier to the lake lying 400 metres beneath. As the glacier slides overhead, trace amounts of gases might seep through, but nothing substantial. There’s hardly any oxygen dissolved in the water, and radioactive-dating of the little carbon suggests that it is incredibly old. But despite the extremely salty water and the lack of light, oxygen and carbon, the microbes have lived there for millions of years, using sulphate ions as their only source of energy.