Newswise —
Life in the ocean’s “twilight zone” could decline dramatically due to climate change, new research suggests.
The gloaming realm (200m to 1,000m down) receives minimal illumination yet harbors diverse life forms and billions of tons of organic substance.
The new study warns that climate change could cause a 20-40% reduction in twilight zone life by the end of the century.
In a scenario of elevated emissions, the existence in the gloaming realm might suffer substantial depletion in 150 years, without recuperation for millennia.
"The understanding of the oceanic gloaming realm is still comparatively limited, yet by drawing on historical evidence, we can gain insight into the potential future outcomes," stated Dr. Katherine Crichton, the lead researcher of the study and affiliated with the University of Exeter.
The group of researchers consisted of paleontologists and ocean modelers who analyzed the twilight zone's biodiversity during previous warm periods by examining data obtained from preserved microscopical shells in marine sediments.
"Our investigation focused on two historical warm phases that occurred approximately 50 million and 15 million years ago," stated Professor Paul Pearson, the research leader from Cardiff University.
“We found that the twilight zone was not always a rich habitat full of life.
"During these warm epochs, the twilight zone's inhabitants were significantly fewer, primarily due to a drastic reduction in the amount of nutrients that descended from the surface waters," explained Professor Pearson.
The organisms inhabiting the gloaming realm mostly rely on consuming organic matter particles that have descended from the ocean's surface.
The study's findings indicated that in previous eras with elevated ocean temperatures, bacteria decomposed the organic matter at a faster pace, leading to a reduction in the amount of food that reached the gloaming realm.
Dr. Crichton highlighted that the diverse range of organisms in the twilight zone evolved in the recent few million years due to the ocean water's cooling, which functioned similar to a refrigerator, lengthening the organic matter's preservation and creating better conditions for the thriving of life.
This inquiry urged the researchers to ponder over the future of the gloaming realm's inhabitants in a world with rising temperatures.
By combining data from past warm periods with simulations using Earth System Models, the researchers modeled the possible scenarios occurring in the present gloaming realm and projected the potential outcomes in the upcoming decades, centuries, and millennia due to climate warming that results from greenhouse gas emissions.
Dr. Crichton added, "Our study indicates that considerable changes may already be in progress."
"Unless we act promptly to diminish greenhouse gas emissions, the gloaming realm's organisms could face the prospect of vanishing or becoming extinct in as little as 150 years, and the consequences could linger for millennia," warned Dr. Crichton.
"Even a future with low emissions may inflict a substantial impact, but the severity would be far less compared to the outcomes of medium and high-emission scenarios," added Dr. Crichton.
Dr. Crichton emphasized that their study serves as an initial stage in discovering the twilight zone's susceptibility to climate warming.
The study's three emissions scenarios are defined based on the cumulative carbon dioxide emissions that occurred after 2010. The "low" scenario includes 625 billion tonnes, the "medium" scenario comprises 2,500 billion tonnes, and the "high" scenario encompasses 5,000 billion tonnes.
To provide context, the University of Exeter-led Global Carbon Budget projected the total global carbon dioxide emissions to be around 40.6 billion tonnes for the year 2022 alone.
As per the Global Carbon Budget, the yearly carbon dioxide emissions have been close to 40 billion tonnes from 2010 to 2022. Therefore, the majority of the carbon dioxide emissions, which approximately amount to 500 billion tonnes, for the "low" scenario outlined in the study have already been released.
At the current rate, the “medium” scenario would be reached 50 years from now, and the “high” in just over a century.
Dr. Jamie Wilson from the University of Liverpool commented that the twilight zone performs a crucial function in the ocean's carbon cycle since the majority of the carbon dioxide that phytoplankton consume ultimately finds its way there as their remains sink down from the ocean's surface.
One of the hurdles in forecasting how carbon movement could alter in the coming years is the abundance of processes to unravel in the contemporary ocean.
By retrospectively examining the twilight zone during prior warm periods, we can ascertain the most significant mechanisms and apply them to prognosticate the future.
Our findings suggest that this inherent carbon cycle is probable to be undergoing alterations currently and could be disrupted for a considerable duration in the future.
“We found that this natural cycling of carbon is likely already changing and may be perturbed long into the future."
To enhance our comprehension of the ocean's twilight zone, a UN initiative (JETZON) has been established, recognizing that it remains inadequately understood from almost every viewpoint. Nevertheless, it is home to conceivably the planet's most extensive and underutilized fish stock and recirculates roughly 80% of the organic matter that descends from the fertile surface waters.
The recent investigation was financially supported by the Natural Environment Research Council and involved scholars from Exeter, Liverpool, California Riverside, Bremen, Cardiff, and University College London.
The article, which was published in the journal Nature Communications, bears the title: "What the geological past can tell us about the future of the ocean's twilight zone."
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