Gulf of Mexico was spared from ancient mass extinction

A new study led by the University of Texas at Austin has found that an ancient bout of global warming 56 million years ago that acidified oceans and wiped-out a wide range of marine life had a milder effect in the Gulf of Mexico, where life was protected by the basin’s unique geology. Besides shedding new light on an ancient mass extinction, these findings could help scientists predict how current climate change will affect marine life.

“This event known as the Paleocene-Eocene Thermal Maximum or PETM is very important to understand because it’s pointing towards a very powerful, albeit brief, injection of carbon into the atmosphere that’s akin to what’s happening now,” said study lead author Robert Cunningham, a geochemist at the University of Texas Institute of Geophysics (UTIG).

Dr. Cunningham and his colleagues investigated the impact of this ancient period of global warming on the Gulf of Mexico by studying a group of sand, mud, and limestone deposits found across the area. They found an abundance of microfossils from radiolarians, a type of plankton that seemed to have thrived in the Gulf during that period. This discovery suggests that a steady supply of river sediments and circulating ocean waters had helped radiolarians and other local microorganisms survive while our planet’s climate became largely hostile to marine life.

“In a lot of places, the ocean was absolutely uninhabitable for anything,” said study co-author Marcie Purkey Phillips, a biostratigrapher at UTIG. “But we just don’t seem to see as severe an effect in the Gulf of Mexico as has been seen elsewhere.”

According to the scientists, the Gulf was largely spared because about 20 million years before the ancient global warming, the rise of the Rocky Mountains had redirected rivers into the northwestern part of the Gulf (a tectonic shift called “the Laramide uplift”), sending much of the continent’s rivers through what are now Texas and Louisiana into the Gulf’s deeper waters. When North America became hotter and wetter, the rain-filled rivers transported nutrients and sediments into the basin, providing sufficient sustenance for phytoplankton and other marine life-forms. These findings also confirm that the Gulf remained connected to the Atlantic Ocean and the salinity of its waters have never reached the extremes seen elsewhere.  

Clarifying how the water and ecology of the Gulf changed during a period of intense climate change could help scientists better understand and predict the effects of today’s global warming on this unique region, as well as on other similar areas.

The study is published in the journal Marine and Petroleum Geology.

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By Andrei Ionescu, Earth.com Staff Writer