January 6, 2020
Iron-rich aerosols from the 2019-2020 fires fertilized big phytoplankton populations in the far South Pacific.
The devastating wildfires that scorched eucalyptus forests in eastern and southern Australia in the summer of 2019-2020 were unprecedented in their scale and strength. Started in October 2019 and burning through January 2020, they blistered countless hectares and killed or displaced an estimated 3 billion animals. The fires gave off large amounts of carbon dioxide and lofted smoke plumes to record heights.
That smoky summer also affected marine communities countless kilometers away, according to brand-new research that integrated satellite information and surface measurements. From December 2019 to March 2020, the deposition of aerosols released by the fires set off phytoplankton flowers in the normally iron-limited waters of the South Pacific and Southern Ocean. Together the surface location of those flowers surpassed the size of Australia.
To measure the aerosols produced by the fires, the team analyzed aerosol optical depth (AOD) data from the Copernicus Atmosphere Monitoring Service (CAMS), which is based partly on measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASAs Terra and Aqua satellites. The researchers looked particularly at black carbon AOD as a proxy for wildfire aerosols. Those chlorophyll abnormalities took place within a few days to weeks after the peaks in black carbon aerosols. In those two regions, black carbon aerosol worths were likewise 300 percent higher than regular, a level unmatched in the 17-year aerosol record.
Analyses of air-borne aerosol samples gathered there exposed the presence of iron and a saccharide molecule called levoglucosan that forms when cellulose burns– direct evidence that the aerosols came from the wildfires.
The image above, acquired on January 6, 2020, by the Japanese satellite Himawari-8, shows the plume of smoke and ash streaming far from the fires on the southeastern coast of Australia. As worldwide environment warms, such fires are expected to increase in frequency and strength, releasing more co2, which further fuels climate change.
It is essential to comprehend the effects of such fires, not just on local ecosystems however on distant ones as well, noted marine biogeochemist Weiyi Tang of Princeton and biogeochemist Nicolas Cassar of Duke University, lead authors of the research study. “The truth that both the fires and the blossoms were extraordinary in the satellite record initially provided us an idea that they might be linked,” Cassar said.
To quantify the aerosols discharged by the fires, the group examined aerosol optical depth (AOD) information from the Copernicus Atmosphere Monitoring Service (CAMS), which is based partly on measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASAs Terra and Aqua satellites. In the noticeable spectrum, AOD offers a step of the amount of desert dust, sea salt, sulfate, organic matter, and black carbon in a column of air. The researchers looked particularly at black carbon AOD as a proxy for wildfire aerosols. Tang, Cassar, and coworkers found that black carbon emissions emanated primarily from wildfires in southern and eastern Australia and burnt out to the broad South Pacific within a couple of days.
2019– 2020
The group also examined chlorophyll concentrations recorded by the European Space Agencys Ocean Color Climate Change Initiative. OCCI merges information from the Medium Resolution Imaging Spectrometer (MERIS) on Envisat, Terra MODIS, the Visible Infrared Imaging Radiometer Suite (VIIRS), and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS).
Those chlorophyll anomalies happened within a few days to weeks after the peaks in black carbon aerosols. In those 2 areas, black carbon aerosol worths were likewise 300 percent higher than normal, a level extraordinary in the 17-year aerosol record.
As the wildfire plumes streamed off the Australian continent, they passed over an air sampling station on the top of Mount Wellington in Tasmania. Analyses of airborne aerosol samples gathered there revealed the existence of iron and a saccharide particle called levoglucosan that forms when cellulose burns– direct evidence that the aerosols came from the wildfires. Downwind, Argo drifts in the ocean also detected elevated levels of chlorophyll in the flower locations, verifying that the satellite chlorophyll signal was genuine.
The connection in between the smoke aerosols and the bloom was also corroborated by a design that calculated the trajectories of the air parcels leaving the fire. “The aerosol optical depth and the designed air mass trajectories verified that the algal flowers remained in the path of the aerosols from the wildfires,” Cassar said.
The team even thought about whether natural variability in the ocean– such as the Indian Ocean Dipole, the Southern Annular Mode, or El Niño-Southern Oscillation– could explain the increase of nutrients sustaining the blossom. “There was nothing that might describe the observations that we had,” Tang stated. “It ends up that natural irregularity was fairly little compared to what we observed.”
January 4, 2020
In an associated paper, another research group reported that the 2019-2020 fires released more than twice the carbon dioxide previously estimated, a magnitude exceeding Australias annual carbon dioxide emissions from fires and fossil fuels. The phytoplankton bloom initially took up a terrific deal of that carbon dioxide, but its supreme fate– for example, whether it was respired at the surface or exported to the deep ocean– is not yet known. “For us, the holy grail is to figure out just how much this bloom balanced out the carbon emissions related to the Australian wildfires,” Cassar said.
Illuminating the links amongst wildfires, climatic carbon dioxide, and marine ecosystems might help enhance global carbon cycle models. “We focused on the Australian wildfires due to the fact that they were truly special in size, but I think its worth likewise looking at other wildfires, including in California, and other areas of the world,” Cassar noted. “And if it is important, globally, then it requires to be better represented in Earth system models.”
NASA Earth Observatory images by Joshua Stevens, using information thanks to Tang, W., et al. (2021) consisting of information from the European Space Agency, and MODIS information from NASA EOSDIS LANCE and GIBS/Worldview. Himawari imagery courtesy of the Japan Meteorological Agency.
By Sara E. Pratt, NASA Earth Observatory
November 6, 2021