Impact of volcanic ash on marine algae and the global carbon cycle

Volcanic ash fertilization of iron-limited phytoplankton in remote marine waters has been suggested to perturb global biogeochemical cycles and climate. For example, ash from the Pinatubo (Philippines) eruption in 1991 was suggested to have fertilized vast areas of the iron-limited Southern Ocean – potentially causing the drawdown in atmospheric carbon dioxide observed subsequently. However, until recently the impact of volcanic ash on phytoplankton communities in the Southern Ocean had never been directly tested.

Browning and co-authors conducted over 20 experiments in the South Atlantic and Southern Ocean where they added small quantities of volcanic ash to natural phytoplankton communities incubated in bottles. The responses they observed led to two important findings: (i) they conclusively demonstrated for the first time that volcanic ash deposition events strongly stimulated phytoplankton in the Southern Ocean; and (ii) at several experimental locations phytoplankton responded significantly to supply of volcanic ash, but not to iron only. This latter finding could be particularly important as it suggests phytoplankton at these sites may have been limited by another micronutrient other than iron. Manganese concentrations at these sites were amongst some of the lowest ever recorded in seawater and Browning and co-authors therefore suggested that the enhanced response to ash may have likely been a result of relieving manganese (co)limitation.

Both of these findings could both have important implications for our understanding of marine biogeochemistry in the Southern Ocean. Firstly, the Southern Atlantic and Drake Passage, where the experiments were conducted, are areas highly prone to ash deposition from explosive volcanic eruptions in South America – suggesting that ash-driven fertilization and potential carbon export from these waters could be an important control on the biogeochemistry of the region. Secondly, if manganese is (co)limiting marine algae in these waters, addition of this element alongside iron might be critical for stimulating phytoplankton blooms in the region.

14 Browning low

Figure: Maps showing the sites where experiments were conducted, highlighting the nutrient concentrations measured in seawater (warmer colors represent higher nutrient concentrations) and the response of phytoplankton to iron and ash additions (warmer colors represent larger phytoplankton responses). For (d-e) sites where the phytoplankton response was statistically significant (relative to bottles where no treatment was made) are shown with black outlines. Please click here to view the figure larger.

 

Reference:

Browning, T. J., Bouman, H. A., Henderson, G. M., Mather, T. A., Pyle, D. M., Schlosser, C., Woodward, E. M. S., Moore, C. M. (2014). Strong responses of Southern Ocean phytoplankton communities to volcanic ash. Geophysical Research Letters, 41(8), 2851–2857. doi:10.1002/2014GL059364 Please click here to access the paper.

Latest highlights

Science Highlights

Loss of old Arctic sea ice increases methylmercury concentrations

Researchers from the SCRIPPS, the Stockholm Natural Museum and the Mediterranean Institute of Oceanography show the importance of sea ice composition on methylmercury budgets

02.09.2020

Science Highlights

Estimating Atmospheric Trace Element Deposition Over the Global Ocean

A recently developed method based on the natural radionuclide Be-7 has provided a means to estimate the bulk atmospheric trace element deposition velocity

Science Highlights

Dissolved gallium unravels Pacific and Atlantic waters in the Arctic Ocean

Whitmore and co-workers demonstrate that the dissolved gallium distribution provide a better water source deconvolution than the nutrient tracers

22.07.2020

Science Highlights

Precise estimate of the mercury export from the Arctic to the Atlantic Ocean

Using new observations acquired during GEOTRACES Arctic cruises, a refined arctic mercury budget has been established

21.07.2020

Rechercher