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
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.