The study, which today features in the international journal Nature Geoscience, suggests that fjords worldwide are major carbon sinks that can bury about 18 million tonnes of organic carbon -- equivalent to 11 per cent of annual marine carbon burial globally.
Fjords are long, deep and narrow estuaries formed at high latitudes during glacial periods as advancing glaciers incise major valleys near the coast, and are found in northwestern Europe, Greenland, North America, Antarctica and in our South Island.
But as deep and often low oxygen marine environments, fjords can also provide stable sites for carbon-rich sediments to accumulate, said study co-author Dr Candida Savage, of the University of Otago.
Carbon burial is an important natural process that provides the largest carbon sink on the planet and influences atmospheric carbon dioxide (CO2) levels at multi-thousand-year time scales.
In their research, Dr Savage and her colleagues calculated that per unit area, fjord organic carbon burial rates are twice were large as the ocean average.
"Therefore, even though they account for only 0.1 per cent of the surface area of oceans globally, fjords act as hotspots for organic carbon burial," Dr Savage said.
The researchers suggest that fjords may play an especially important role as a driver of atmospheric CO2 levels during times when ice sheets are advancing or retreating.
The Earth is currently in an interglacial period after ice sheets receded around 11,700 years ago.
During glacial retreats, fjords would trap and prevent large volumes of organic carbon flowing out to the continental shelf, where chemical processes would have caused CO2 to be produced, Dr Savage said.
Once glaciers started advancing again this material would likely then be pushed out onto the shelf and CO2 production would increase.
"In essence, fjords appear to act as a major temporary storage site for organic carbon in between glacial periods," she said.
"This finding has important implications for improving our understanding of global carbon cycling and climate change."
The research involved fieldwork in Fiordland and analysing data from 573 surface sediment samples and 124 sediment cores from fjords around the world.
By Jamie Morton of the New Zealand Herald
