Phytoplankton flourishes as Kasatochi’s ash fertilizes the ocean

The eruption of Alaska’s Kasatochi volcano in August 2008 has led to a surge in the population of phytoplankton in the North Pacific, says a paper in Geophysical Research Letters authored by a horde of scientists from institutions in Canada, the USA and the UK, led by oceanographer Roberta C. Hamme of the University of Victoria, British Columbia. An unusual storm system meant that the ash deposited by the volcano was transported across a very wide area of the north-eastern Pacific, and the iron content encouraged the growth of phytoplankton (for which iron is a key nutrient), producing one of the largest plankton blooms ever recorded in this region. Scientists have recently suggested that volcanic ash fertilization of the ocean in this way can occur, but, as Professor Hamme notes in the very useful summary of the Kasatochi paper she has made available as a PDF on her website (wish more scientists would do that), this is the first time conclusive evidence has been obtained to support the hypothesis.

Because phytoplankton (which are the basis of oceanic and freshwater food chains) consume carbon dioxide and release oxygen, seeding the oceans with iron to encourage their growth has sometimes been suggested as a means of diminishing atmospheric CO2. However, the evidence of the naturally-occurring Kasatochi seeding episode is that the process is not very efficient and that it would take a lot of iron to make even a small difference.

• Roberta C. Hamme et al. ‘Volcanic ash fuels anomalous plankton bloom in subarctic northeast Pacific’, Geophysical Research Letters, 37 (2010), doi:10.1029/2010GL044629. [abstract]

News
How volcanoes feed plankton – ScienceNow, 5 October 2010
Effects of volcanic eruption dash promising global warming theory – Globe and Mail, 5 October 2010
Volcano ‘seeded’ ocean bloom – UPI.com, 6 October 2010