Icelandic Volcano with the difficult name, Eyjafjallajökull’s iron-rich ash fertilized North Atlantic Ocean
In about a third of the global ocean, the abundance of life is limited by a dearth of biologically available iron.
The supply of iron to a region that is depleted in this important nutrient can be replenished to stimulate algal productivity, and can result in a temporary boom in biological activity.
For much of the surface ocean, the wind-borne transport of iron-rich dust and the upwelling of nutrient-filled water are the major sources of iron. Another potentially important source is the deposition of the iron-rich ash produced by volcanic eruptions.
Though satellite observations and modeling work suggest that volcanic ash could seed life in such a way, there have been only a limited number of direct observations of the effects of ash deposition on surface ocean waters.
Thanks to a bit of serendipitous scheduling, Achterberg et al. conducted a series of research cruises in the Iceland Basin region of the North Atlantic Ocean both during and after the month-long eruption of Iceland’s Eyjafjallajökull volcano in the spring of 2010.
In April 2010, the eruption sent an ash plume kilometres into the atmosphere, resulting in ash/dust blowing in the wind and being deposited across up to 570,000 sq km of the North Atlantic Ocean.
The five-week volcanic activity was still ongoing when a team of researchers arrived in the Iceland Basin region aboard a research vessel.
“Our study was unique in the sense that we were the first to undertake sampling at sea of volcanic ash deposition and the chemical and biological effects in the surface ocean,” explained lead author Eric Achterberg from the National Oceanography Centre Southampton, UK.
“In addition, we were able to sample the ocean region again a few months after the eruption and observe the changes since the eruption.
“The opportunity to sample during the eruption and also a couple of months after the event allowed us to obtain a unique insight into the effects of the ash deposition on the biology and chemistry of the Iceland Basin.”
Three years earlier, the team had shown that the production of phytoplankton – microscopic plants that form a key component of marine food chains – was limited by the availability of dissolved iron, which was essential for the tiny plants’ growth.
Three cruises allowed the authors to undertake measurements of surface ocean iron concentration before, during, and after the eruption in a region directly affected by the towering ash plume. Beneath the plume, the authors found peak dissolved iron concentrations up to 10.2 nanomolar, compared to 0.23 to 0.45 nanomolar detected before ash deposition.
Using a model of the ash plume trajectory and ash deposition rates, along with measurements of iron dissolution, the authors calculated that up to 570,000 square kilometers (220,000 square miles) of North Atlantic waters could have been seeded with at least 0.2 nanomolar of iron. In controlled biological incubation experiments, the authors added volcanic ash collected under the plume to sea water, and find that iron leached from the ash could drive an increase in biological productivity and a draw-down of nutrient levels.
Using the data from our work on the Haida Salmon project, which by the way is the best data set on the planet on the power of dust and iron in ocean plankton ecology, we calculate that not less than 400 million tonnes of CO2 was converted into phytoplankton, that’s fish food!
Reference to the paper mentioned above – Title: Natural iron fertilisation by the Eyjafjallajökull volcanic eruption,Eric P. Achterberg, C. Mark Moore, Stephanie A. Henson, Sebastian Steigenberger, Lizeth C. Avendano, Michael Cassidy, Debbie Hembury, Jessica K. Klar, Anna I. Macey, Chris M. Marsay and Thomas J. Ryan-Keogh: National Oceanography Centre Southampton, University of Southampton, European Way, Southampton, United Kingdom; Andreas Stohl and Sabine Eckhardt: Norwegian Institute for Air Research, Instituttveien 18, Kjeller, Norway; Michael I. Lucas: Marine Research Institute, University of Cape Town, Rondebosch, South Africa, Geophysical Research Letters, doi:10.1002/grl.50221, 2013