A new study shows that rising temperatures could drive plankton and other tiny oceanic organisms toward a carbon threshold, potentially exacerbating global warming. Recent studies emphasise that it’s important to act before such climate tipping points are reached.
Scientists from Duke University and the University of California, Santa Barbara, US, have shown that a significant majority of global oceanic plankton, along with many tiny organisms in lakes, peatlands, and other ecosystems, might reach a tipping point, according to a press statement by Duke University published in SciTechDaily. The study, published in Functional Ecology, shows that increasing heat levels could lead to changes in how microbes interact with carbon dioxide. Instead of absorbing it, they could do the opposite, a result of how their metabolism responds to the rise in temperature of the water bodies.
As carbon dioxide is a greenhouse gas, this could further increase the temperature and cause runaway change, wherein small amounts of warming have a significant impact, according to the statement. For this study, the researchers focused on tiny organisms called mixotrophs which have two modes of metabolism: they can photosynthesise like a plant or hunt food like an animal, depending on conditions. Most of the plankton in the oceans are mixotrophs.
“Because mixotrophs can both capture and emit carbon dioxide, they’re like ‘switches’ that could either help reduce climate change or make it worse,” co-author Holly Moeller, an assistant professor at the University of California, Santa Barbara said in the statement. During photosynthesis, they absorb carbon dioxide and while eating eat, they release carbon dioxide. Through the stud, the researchers have demonstrated that as the temperature increases, more mixotrophs rely on eating food than making their own through photosynthesis. This shifts the balance between carbon taken in and carbon released into the atmosphere.
The study models show that, eventually, these microbes could reach a tipping point, a threshold beyond which they suddenly shift from carbon sink to carbon source. The tipping point is difficult to undo and if they cross it, it would require significant cooling — more than one degree Celsius — to restore their cooling effects, according to the statement.
The researchers suggest that it could be possible to spot the shifts in advance and address them before the tipping point is reached. However, the detection of early warning in reaching the tipping point depends on a key factor: nutrient pollution.
Discharges from wastewater treatment facilities and water with significant chemical fertilizers can send nutrients such as nitrate and phosphate into lakes and streams and coastal waters. The study model showed that high amounts of these nutrients reduce the early signals and eventually it disappears, and the tipping point arrives without earning.