Farewell 40% of marine life if it does not “snow” more in the oceanic twilight zone

A study in Nature Communications calculates the impact of climate on available nutrients in the oceanic twilight zone

– A warmer sea means a sea less rich in food. And more risk of extinction for many marine species. Those living in the so-called oceanic twilight zone, that is, the portion of water column between 200 and 1000 meters deep. This is stated by a study, recently published in Nature Communications, that reconstructed the variations of nutrients in these regions of the oceans during periods when the Earth’s climate was warmer than today, in the Cenozoic.

The oceanic twilight zone is named for the low amount of solar radiation that can penetrate those depths. The organisms that populate it depend on the organic matter that comes from the upper layers. In jargon it is called “sea snow”: debris, remains of algae and plankton, excrement of fish, organic and inorganic matter rich in nutrients that allows life in the oceanic twilight zone.

How nutrients change in the oceanic twilight zone

Sea snow is the excellent victim of the climate crisis in the oceans. According to the authors of the study, warmer temperatures decrease the amount of substances that sink into the lower oceanic layers. Even in a very favorable emissive scenario, the expected nutrient drop in the next 100-200 years is 20%. In more plausible scenarios and close to the current climate trajectory, the reduction can reach up to 50%.

Numbers that involve radical changes in the ecology of the oceanic crepuscular zone. By the end of this century, the different availability of food could reduce marine life in this mesopelagic belt by 20-40%. Changes, however, that are already underway, warn the authors of the study. Stopping them and reversing the course could take several thousand years.
“Our findings suggest that significant changes may already be underway,” explains Katherine Crichton, before signing the study. “Unless we reduce greenhouse gas emissions quickly, this could lead to the disappearance or extinction of much of the life of the twilight zone within 150 years, with effects that extend over millennia”.