Everything cycles

Posted on: February 2, 2022 at 16:46:59 CT

An increasingly popular method to deduce historic sea surface temperatures uses sediment-entombed bodies of marine archaea, one of Earth's most ancient and resilient creatures, as a 150-million-year record of ocean temperatures. While other measures have gaps, this one is increasingly popular because it promises to fill in gaps to provide a near-global record of ocean temperatures going back to the age of the dinosaurs.

But University of Washington research shows this measure has a major hitch: The single-celled organism's growth varies based on changes in ocean oxygen levels. Results published in August in the Proceedings of the National Academy of Sciencesshow that oxygen deprivation can alter the temperature calculations by as much as 21 degrees Celsius.

"It turned out that oxygen has a huge, dramatic effect," said corresponding author Anitra Ingalls, a UW associate professor of oceanography. "It's a big problem."

Recent research shows these archaea, which draw energy from mere whiffs of ammonia, make up about 20 percent of microbial life in the oceans. Their bodies are plentiful in the ocean floor.

A method established in 2002 uses fats in the archaea's cell membrane to measure past ocean temperatures, including during amajor warming event about 56 million years ago that is one of the best historical analogs for present-day climate change, and asudden oceanic cooling of up to 11 degrees Celsius during a period of low ocean oxygen about 100 million years ago, when other records are scarce.