Hawaii & Alaska
GEOTRACES researchers prepare to sample cobalt and more. Credit: Bill Schmoker, PolarTREC. (Photo courtesy: University of Hawai‘i)

HI - New study highlights historical ocean oxygen loss, future possibilities for Fisheries

As the climate warms, there is major concern that Earth’s oceans will lose oxygen. A study published by oceanographers at the University of Hawai‘i at Mānoa revealed that locked in ancient deep-sea sediments is evidence for oxygen loss in the world’s ocean during past glacial periods.

Scientists first measured oxygen in the oceans in the 1960s. Since then, they have observed decreasing levels in the mid-depths of the ocean—a phenomenon that can be explained in part by the fact that warmer waters hold less oxygen.

Less oxygen in the water can lead to habitat loss for fish and other marine species that need oxygen to breathe. If the naturally-occurring low-oxygen regions in the Eastern Pacific expand in a warmer climate, Pacific Island fisheries could be significantly impacted.

Deep sea sediments revealed ocean conditions from the past 145,000 years. (Photo courtesy: Rhea Foreman/University of Hawai‘i)

The study also indicates that widespread oxygen loss with current climate change may not be permanent, if Pacific Ocean currents rearrange in the future.

“Ultimately, it would be helpful if we knew how low-oxygen regions of the ocean changed with past climate changes,” said Nick Hawco, lead author of the study and assistant professor of oceanography, in the University of Hawaiʻi at Mānoa School of Ocean and Earth Science and Technology  “However, the problem is that oxygen is a gas, so we don’t have any reservoirs of past oceans to test the oxygen content. Our new study builds off of prior work where we discovered that low oxygen water bodies in the Pacific are enriched in the metal cobalt.”

Cobalt across the Pacific Ocean (red=high Co, blue=low Co). (Photo courtesy: GEOTRACES)

“One of the biggest sources of cobalt to the oceans is where oxygen deficient zones intersect with the continental shelf, leach cobalt from the shelf, and then transport it across the ocean in a plume of low oxygen water,” said Rhea Foreman, study co-author and oceanography researcher in the University of Hawaiʻi at Mānoa School of Ocean and Earth Science and Technology. “The cobalt is subsequently incorporated into minerals that are deposited onto the seafloor and preserved in the sedimentary record.”

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