Scientists have only recently discovered that Arctic/glacial meltwater streams take in atmospheric carbon at a faster rate than tropical rainforests. Previously scientists have assumed that rivers were a source of carbon rather than a sink. The results were based on tests carried out on Ellesmere Island in Nunavut territory, Canada, the Rocky Mountains and in Greenland. Scientists studied the effects of glacial meltwater running into rivers and lakes downstream.

In temperate rivers high levels of organic matter in rivers leads to high rates of decomposition, causing rivers to larger amounts of carbon dioxide into the atmosphere than they absorb. In contrast, meltwater streams produce little carbon output. In addition, silicate and carbonate sediment from the glaciers causes weathering/chemical erosion in the river. As a result of chemical weathering, there is removal of carbon dioxide from the atmosphere from twenty miles from the river’s source. Thus, during periods of increased melting, glacial rivers can absorb 40 times as much carbon dioxide as the Amazon rainforest. On a per metre squared basis, the rivers can absorb a huge amount of carbon dioxide but given their limited extent, the total amount of carbon dioxide absorbed is much smaller than the Amazon rainforest.

Although scientists have only recently discovered the storage potential of rivers and oceans, this is not a new phenomenon, but one that has been happening for a long time, and so does not offer a ’new’ potential carbon sink. The benefits, however, may only be short-term in some glacial areas. As  glaciers around the world melt, the annual meltwater may decrease in decades to come, and so the benefits of meltwater as a carbon sink may be reduced. Glaciers are a finite resource, as is the meltwater that comes from them. Global heating is occurring at a higher rate in high latitudes compared with anywhere else on Earth and the implications for the world’s ice stores are clear.