A Bloom as Big as Australia
A brilliant paper recently appeared in Nature (Tang et al 2021).
Sometimes, big bushfires distribute nutrients such as iron and nitrates to barren areas of the ocean. This creates blooms of plankton which absorb CO2 from the atmosphere. Admittedly much of this may well be re-emitted to the atmosphere once the bloom is over but a good deal will be removed from the system forever as it sinks to the bottom of the ocean in the form of faecal pellets and the skeletons of the animals which graze the plankton.
The above map shows the plankton bloom due to the 2019/20 Australian bushfires derived from satellite imagery of ocean colour. According the paper:
Satellite-estimated marine net primary production (NPP) and export production (EP) increased substantially during the 2019–2020 Australian wildfire season compared with the monthly climatologies, corresponding to a cumulative net additional uptake of ~186 ± 90 Tg C from October 2019 to April 2020, equivalent to ~95 ± 46% of the CO2 emission (~195 Tg C) from the 2019–2020 Australian wildfires.
Given that we can expect at least a 90% recovery from these fires, we conclude that, in the long run, these bushfires will have caused a net absorption of atmospheric CO2, viz.: 90% recovered on land and 95 ± 46% exported from the atmosphere to the deep ocean by the plankton bloom.
Because of this plankton bloom, the 2019/20 bushfires brought about the removal of nearly twice the amount of CO2 from the atmosphere that they put into it.
Widespread phytoplankton blooms triggered by 2019–2020 Australian wildfires. Weiyi Tang, Joan Llort, Jakob Weis, Morgane M. G. Perron, Sara Basart, Zuchuan Li, Shubha Sathyendranath, Thomas Jackson, Estrella Sanz Rodriguez, Bernadette C. Proemse, Andrew R. Bowie, Christina Schallenberg, Peter G. Strutton, Richard Matear, Nicolas Cassar. Nature 597, 370-389 (2021).
1 Tg = 1012 g = 1 million tonnes.
“Climatologies” means “usual monthly averages”.
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