Adapted from an article in New Scientist, 29 August 2015
The meltwater beneath Greenland’s glaciers is an important source of the silicon that some plankton need to build their glassy skeletons but climate change could alter the input.
Plankton called diatoms use the oxidised form of silicon, silica, as they grow. The plankton mop up significant quantities of atmospheric carbon dioxide as they photosynthesise, which they then take to the bottom of the ocean with them when they die – a natural carbon sink.
But large plankton blooms might become less likely to form without the ready supply of silicon.
The base of glaciers is a hotbed of physical and chemical activity as the ice grinds away at the rock below. For instance, we know that the process frees up hundreds of thousands of tonnes of iron that is then carried to the sea in meltwater, fertilising the ocean and allowing plankton to thrive.
Jon Hawkings at the University of Bristol, UK, and his colleagues wondered what else might be transported in the meltwater. Previous work had suggested that the process frees up silicates, so the researchers have begun assessing how much silicon the meltwater dumps into coastal waters.
“It’s early days but our estimates indicate that the ice sheets could be a huge source of silicon to the polar regions,” says Hawkings. Most of this comes from silicon attached to the sediments suspended in the meltwater that on reaching the ocean dissolve into the salt water.
Hawkings says the high abundance of diatoms in Greenland’s coastal waters could be a direct result of the meltwater’s silicon influx. He presented the findings at the Goldschmidt conference in Prague, the Czech Republic, recently, and plans to publish figures detailing the quantities of silicon in meltwater in the next few months.
The worry now is that with climate change affecting glacier melting this process could be changed in unpredictable ways, having an impact on ocean productivity and global carbon fluxes.
“Although more work needs to be done to properly quantify this, we believe it is highly likely these inputs will change in a warming climate,” says Hawkings.
The idea makes sense, says Matt Charette at the Woods Hole Oceanographic Institution in Massachusetts. “It’s certainly possible that the runoff from the Greenland ice sheet may help recharge the ecosystem during summer when meltwater reaches a maximum,” he says.
But the same process might not be as important around Antarctica, where the waters are naturally rich in silica. There, iron is probably the limiting factor on diatom growth, says Charette.