There are serious fears that Earth’s oceans will lose oxygen as the climate warms. A study published in the journal Geophysical Research Letters by oceanographers at the University of Hawaii at Manoa found that evidence of oxygen loss locked in ancient deep-sea sediments in the world’s oceans during past ice ages points to widespread oxygen loss under currents. Changes.

Scientists first measured the oxygen content of the oceans in the 1960s. Since then, they have observed a decrease in oxygen levels in the mid-ocean depths; This can be partially explained by the fact that warmer waters contain less oxygen. Low levels of oxygen in water can lead to loss of habitat for fish and other marine species that need oxygen to breathe. If natural low-oxygen zones in the eastern Pacific expand into a warmer climate, this could seriously impact Pacific island fisheries.

Cobalt holds clues in deep-sea sediments
“Ultimately, it would be useful if we knew how low-oxygen regions of the ocean changed as a result of past climate changes,” said Nick Hauko, lead author of the study and UH Mānoa Ocean School associate professor of oceanography. and Earth Sciences and Technology (SOEST).

“But the problem is that oxygen is a gas, so we don’t have reservoirs from past oceans to test oxygen content. Our new study builds on previous studies where we found that low-oxygen waters in the Pacific Ocean are rich in the metal cobalt.”

“One of the largest sources of cobalt in the oceans is where oxygen-deficient areas intersect with the continental shelf, where cobalt leaches from the shelf and is then transported across the ocean as a cloud of low-oxygen water,” said Rhea Forman. -author of the research. – Oceanographer and researcher at SOEST. “Cobalt is then incorporated into minerals that accumulate on the seafloor and are stored in sedimentary rocks.”

The researchers analyzed seafloor sediments from the last 145,000 years, a period that includes the last great ice age. They found more cobalt in sediments from past ice ages compared to more recent sediments.

“This means that there was an accumulation of cobalt in the Pacific Ocean during the last ice age,” Houko said. “Since high cobalt is an indicator or proxy for low oxygen, this suggests that larger low-oxygen zones were likely present in the Pacific at that time.”

Time to adapt

One proposed explanation for low-oxygen waters being more common in cold climates is the change in ocean circulation that accompanies climate change. Today, complex currents flowing from west to east help oxygenate the mid-depth waters of the tropical Pacific Ocean.

“If these currents weaken, the oxygen content of the Pacific Ocean will decrease,” Houko said. “We think this is exactly what happened during the last ice age. But we don’t know how strongly or how quickly these currents will respond to ocean warming.”

This could mean that fish and other species can adapt to changes in oxygen content if these changes occur slowly enough, as they did in the past.

“Looking at carbon emissions over the last 150 years, we need to cut emissions as quickly as possible to buy time for these ecosystems to adapt to the climate change we are currently in,” Houko added. Source