Between September 2019 and March
2020, wildfires killed billions of animals and decimated more than 200,000
square kilometers of Australian forest, an area larger than the size of Nebraska.
Some thousands of kilometers away, in the Southern Ocean,
massive algae blooms covering a surface larger than the area of Australia itself.
Just how are these wildfires and ocean blooms connected?
To untangle that, we look to the carbon cycle.
The carbon cycle is the flow of carbon between reservoirs
in the atmosphere, plants and animals, land and ocean.
It's one of the key processes that keeps life sustainable on Earth.
And at the heart of all this are land plants and aquatic phytoplankton.
On land, most carbon is stored in forests.
Here, plants absorb carbon dioxide from the atmosphere into their cells.
With energy from the Sun
plants combine carbon dioxide and water to form carbohydrates, such as sugar,
and oxygen through photosynthesis.
In this process, carbon dioxide is converted to carbon-based
cellular material.
Carbon stored in those plants can be transferred when animals eat
the plants, the plants die and decay,
or, in the case of Australia, fire consumes the plants.
And once again, carbon based cellular material becomes
carbon dioxide that ends up in the atmosphere.
If we look to the ocean reservoir, carbon dioxide is also absorbed
by phytoplankton, microscopic organisms that convert carbon dioxide, water
and sunlight into carbohydrates like sugar and oxygen through photosynthesis.
Carbon dioxide released into the atmosphere
eventually becomes available for aquatic photosynthesis.
In general, any change that shifts carbon out of one reservoir
puts more into other reservoirs.
But photosynthesis also requires
nutrients such as nitrogen, phosphorus and iron.
Without the right proportions of these nutrients,
photosynthesis doesn't happen, which can be seen in
the iron-limited parts of the ocean, such as far offshore of Australia.
Atmospheric aerosols released by fires, however, contain carbon
as well as other nutrients essential for plant growth like iron.
When these aerosols are deposited on the ocean's surface,
these nutrients become available for photosynthesis.
This iron from the Australian wildfires is now thought to have stimulated
the massive southern Ocean phytoplankton blooms, blooms of such magnitude
that they converted an almost equivalent volume of carbon dioxide
released by the fires into carbohydrate and cellular material.
And here is why having a
vantage point from space is crucial.
From satellites, we can observe how the movement of carbon changes
when large scale events like wildfires occur.
The connection between the Australian wildfires and Southern Ocean
bloom could not have been made without satellites.
NASA's Plankton, Aerosol, Cloud, and ocean Ecosystem, or PACE,
mission, is specifically designed to better measure parts of the atmosphere
and ocean connection with unprecedented resolution.
PACE’s instruments will shed new light on the composition and distribution
of these massive mixtures of tiny aerosol particles and aquatic microorganisms.
Onboard are two polarimeters, instruments that measure specific angles
of light reflected, which, for example, allows researchers to tease apart
the specific type of aerosols in these kinds of massive fire events.
PACE’s flagship sensor, the Ocean Color Instrument, or OCI, will cover vast
swaths of the ocean, measuring concentrations of photosynthetic pigments,
allowing researchers to decipher the different types of phytoplankton.
With an instrument like OCI, where you're measuring
this full spectrum of color, all the colors of the rainbow
you can imagine, we can start teasing apart the species
and the different functional groups and different communities that exist.
The data from PACE will help define those communities,
allowing for clearer connections within the reservoirs of the carbon cycle.
These fires emitted a huge amount of carbon
and other aerosols into the atmosphere, with some estimates suggesting volumes
greater than Australia's annual emissions from fire and fossil fuels combined.
Those aerosols contained essential nutrients that are thought
to have stimulated the rapid growth of phytoplankton in the Southern Ocean.
And these kinds of connections can have big impacts.
It's really important to know
where the carbon is going and where your food source is going.
This is important for not just climate studies, but food security.
The fires that tore through Australia are just one example
of how Earth systems are linked in ways we're only beginning to fully understand.
With data from PACE, we'll get a clearer picture of carbon as it links
land use and fires, atmospheric aerosols and marine communities
and ultimately improves the data we put into climate models.