Climate warming turning oceanic plankton microbes into CO2 emitters: Study
A new study, published in Functional Ecology, has found that climate warming could cause plankton microbes abundantly present in the oceans, to turn from carbon sinks into carbon emitters. Instead of absorbing carbon dioxide, the researchers suggest that increasing temperatures are causing these plankton microbes to emit the same, which could potentially exacerbate the effects of climate change.
Mixotrophs can switch between being autotrophs and heterotrophs
Mixotrophic microbes are widely found in fresh as well as salty water and are estimated to constitute the majority of marine plankton. These microbes are a mix of autotrophs and heterotrophs. Mixotrophs can switch between either- performing photosynthesis like plants or can consume other plankton. They act like a switch and are capable of both capturing or emitting carbon dioxide.
Mixotrophic microbes are changing their nature
Researchers from Duke University and the University of California Santa Barbara, by means of computer modeling, studied how mixotrophic microbes gain energy under warming conditions. As temperatures increased, it was found that mixotrophic microbes turned from being carbon absorbers to carbon emitters. This indicates these microbes could shift from eliciting a net cooling effect on Earth to a net warming effect.
'Mixotrophic microbes could accelerate global warming'
"Our findings reveal mixotrophic microbes are much more important players in ecosystem responses to climate change than previously thought," said Daniel Wieczynski, the lead author of the study from Duke University. "By converting microbial communities to net carbon dioxide sources in response to warming, mixotrophs could further accelerate warming by creating a positive feedback loop between the biosphere and the atmosphere," he added.
Researchers conducted simulations within a 4-degree temperature span
For the study, the team conducted simulations within a 4-degree temperature window, from 19-23 degrees Celsius. In the next five years, it is predicted that the global warming rate is likely to breach the crucial 1.5 degrees Celsius limit for the first time. Further, the warming rates are expected to cross 2-4 degrees before the end of the century.
These microbes may serve as warnings for rapid climate change
What's interesting is that right before mixotrophic microbes switch to emitting carbon dioxide, their numbers go up drastically. Tracking them could thereby indicate turning points in the fight against climate change. "These microbes may act as early indicators of the catastrophic effects of rapid climate change, which is important in ecosystems that are major carbon sinks like peatlands, where mixotrophs are abundant," said Wieczynski.
Presence of certain nutrients may dampen warning signals
These early warning signs of climate change can go unseen when there is an increase in nutrients like nitrogen in the environment. This nutrient rise usually arises from wastewater treatment facilities and agricultural run-offs.
Researchers tested with higher nutrient levels in simulations
When researchers experimented by incorporating higher amounts of such nutrients in the simulation, they found the temperature range over which the fluctuations in mixotrophic microbial populations were seen, started to decrease. Eventually what happens is that the signal disappears and what's supposed to be the tipping point in climate change arrives with no apparent warning, according to the study.
There is room for further improvements in the study
The study was based on "limited empirical evidence" to examine the effect of climate warming on microbial populations. "Although models are powerful tools, theoretical results must ultimately be tested empirically. We strongly advocate for further experimental and observational testing of our results," said Wieczynski.
