There May Be Good News About the Oceans in a Globally Warmed World

A recent study led by Rutgers University and published in Nature indicates that an analysis of oxygen levels in Earth’s oceans could potentially bring some encouraging news about the oceans’ health in a future world affected by global warming.

The study focused on examining ocean sediment and revealed that during the Miocene warm period approximately 16 million years ago, when the Earth experienced higher temperatures than today, there were higher levels of oxygen in a crucial area of the ocean.

This is significant because in recent years, the levels of oxygen that sustain marine life have been declining, leading to concerns about the expansion of oxygen-depleted zones in various parts of the world’s oceans, further endangering marine ecosystems.

Miocene Warm Period Contradicts Present-Day Oxygen Loss in the Eastern Equatorial Pacific

Scientists attribute this trend to climate change-induced rising temperatures, which impact the ocean’s capacity to absorb oxygen from the atmosphere. However, the study’s findings indicate that the eastern equatorial Pacific, which presently harbors the largest oxygen-deficient zone in the oceans, was well-oxygenated during the Miocene warm period, despite the higher global temperatures at that time.

Anya Hess, the study’s lead author and a doctoral student at Rutgers, suggests that the current loss of oxygen may eventually reverse based on these findings. Oxygen loss has been most pronounced in oxygen-deficient zones in recent decades, and these zones are expected to expand and become shallower, posing a threat to fish populations by reducing their habitat.

Nonetheless, there is divergence among climate models regarding how these zones will evolve beyond the year 2100, which motivated the researchers to conduct further investigations.

To assess the accuracy of current climate models, the researchers selected the mid-Miocene period, characterized by climate conditions resembling those projected for the next few centuries in the current era of climate change. They examined ocean sediments deposited during this period in the eastern equatorial Pacific.

Foraminifera Analysis Reveals Oxygen Levels in Prehistoric Oceans

By analyzing the chemical composition of foraminifera, microorganisms found in the water column and preserved as fossilized remains, the scientists were able to determine the oxygen levels in the ancient oceans. They employed several methods, including the use of nitrogen isotopes that react to denitrification, a process occurring only under very low oxygen levels.

The researchers also utilized a comparative analysis of iodine and calcium levels, which provided subtle distinctions between well-oxygenated and moderately well-oxygenated conditions.

The study’s results were unexpected, revealing that the area under investigation was well oxygenated during the peak of the Miocene warm period, even approaching the oxygen levels observed in the open-ocean South Pacific today.

Yair Rosenthal, a Distinguished Professor at Rutgers specializing in marine and Earth sciences, commented that these findings challenge the notion that the loss of oxygen due to solubility, which has occurred in recent decades, represents the complete response of oxygen to climate change.

The study’s other authors include Ken Miller from Rutgers University, Alexandra Auderset and Alfredo Martinez-Garcia from the Max Planck Institute for Chemistry in Germany, Daniel Sigman from Princeton University, and Xiaoli Zhou from Tongji University in China.

Read the original article on Science Daily.

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