Typhoons bury tons of carbon
Typhoon Mindulle approaches Taiwan on 28 June 2004. (Image courtesy Japan National Institute of Informatics)
A single typhoon can carry out almost a year’s worth of physical and chemical weathering on Taiwan, bringing vast amounts of carbon from the soil into the ocean. The finding emerged from an Ohio State University study published in a recent issue of Geology. This NSF-supported research is the first to examine the chemistry of stream water and sediments in the process of being washed to sea in a typhoon.
A group led by OSU’s Anne Carey analyzed the flow of Taiwan’s Choshui River during Typhoon Mindulle in 2004. Carey’s team studies two types of weathering: physical and chemical. Physical weathering happens when organic matter containing carbon adheres to soil that is washed into the ocean. If accompanied by high sediment loads (such as those during typhoons), this material can be subsequently buried and removed from the atmosphere. Chemical weathering happens when silicate rock on the mountainside is exposed to carbon dioxide and water. As dissolved carbon washes out to sea, it can combine with dissolved calcium to form calcium carbonate, which is deposited on the ocean floor and can eventually be embedded in sedimentary rock.
Scientists have long suspected that hurricanes and typhoons bury a lot of carbon, but since the sediment washes out to sea quickly, samples had to be captured during a storm to answer the question definitively. “We discovered that if you miss sampling these storms, then you miss truly understanding the sediment and chemical delivery of these rivers,” says study coauthor and OSU doctoral student Steve Goldsmith.
With collaborators from Academia Sinica, the group dangled water collectors from a bridge over the raging Choshui River every three hours during Mindulle. The sediments were later analyzed for organic carbon and for silica, which allowed the team to infer the amount of chemical weathering. Of the 55 million metric tons of sediment carried out to sea by the Choshui River during Typhoon Mindulle, some 450,000 metric tons consisted of organic carbon particles. That single-storm value is between 72% and 95% of annual values for some of the highest-yielding rivers in the world previously studied by Carey’s group.
Carey cautions that this is the first study of its kind, and more data are needed to put the Mindulle numbers into a long-term perspective. “With two to four typhoons happening in Taiwan per year, it’s not unreasonable to think that the amount of carbon sequestered during these storms could be comparable to the long-term annual carbon flux for the country,” she says.
Ohio State University