With the dramatic temperature and climactic changes across the planet, scientists highlight the importance of understanding the history of the Earth's temperatures to predict what can happen in the future.
Along with tree rings or ice cores, occurrences at the bottom of the Earth's oceans greatly affect changes in climate. To better predict future climactic changes, scientists are conducting studies to measure the temperatures of the world's ancient oceans.
Marine archaea buried over time in sediment tell a lot about the history of ocean temperatures. Found in every ocean on the planet and making up 20 percent of underwater microbial life, the most ancient and resilient organisms, which are 150 million years old, reveal a history of ocean temperatures that date back to when dinosaurs still existed.
Analyzing underwater creatures like the archaea has become a popular method among scientists for understanding historical ocean temperatures. In a new study, researchers from the University of Washington (UW) shed new light on this method, highlighting differences in the growth of these single cell organisms, due to changes in oxygen levels in the ocean.
In a paper published in Proceedings of the National Academy of Sciences, the researchers found that the deprivation of oxygen alters the temperature calculations roughly by 21 degrees Celsius.
"It turned out that oxygen has a huge, dramatic effect," said associate professor of oceanography at UW Anitra Ingalls, and corresponding author of the study. "It's a big problem."
In 2002, a method using fats in the cell membrane of the archaea was established to measure past ocean temperatures, which also included a "major warming event" that occurred 56 million years ago and a "sudden ocean cooling" 100 million years ago when oxygen levels were low, bringing temperatures down to 11 degrees Celsius.
By looking at changes in a temperature proxy called TEX-86 which refers to the 86-carbon lipids found in the cell membrane, the scientists were able to measure ocean temperature. Carbon lipids in the cell membrane track temperatures of surrounding water.
"Changing the oxygen gives us as much as 21 degree Celsius shift in the reading," explained doctoral student in civil and environmental engineering at UW Wei Qin, who is also the first author of the study. "That's solid evidence that it's not just a temperature index."
According to the researchers, the TEX-86 method of measuring past ocean temperatures is inaccurate when applied to parts of the ocean that have been affected by oxygen level changes. Different temperature dependencies can be found in membrane lipids that have different strains. Some may provide accurate past ocean temperature measurements, but some may not.
"The envelope that encloses the cell is sort of the gatekeeper, and when stress is encountered of any kind, that membrane needs to adjust," Ingalls added.
