How the Gulf of Mexico escaped global warming 56 million years ago

The photo above depicts the Mississippi River flowing into the Gulf of Mexico. River sediments and ocean currents helped simple marine life in the Gulf survive a mass deep-ocean extinction 56 million years ago, according to researchers from the University of Texas Institute of Geophysics. years. Credit: US Geological Survey

Research shows how the Gulf of Mexico survived a prehistoric mass extinction.

According to research conducted by the University of Texas Institute of Geophysics (UTIG), an ancient episode of global warming 56 million years ago, which acidified the oceans and wiped out marine life, impacted milder in the Gulf of Mexico, where life was sheltered by the basin. unique geology.

The results, published in the journal Marine and petroleum geologynot only shed light on a prehistoric mass extinction, but can also contribute to attempts to identify oil and gas deposits and help scientists predict how current climate change would affect marine species.

The study’s lead researcher, UTIG geochemist Bob Cunningham, also noted that while the Gulf of Mexico looks significantly different today, there are still important lessons to be learned about climate change today.

“This event known as the Paleocene-Eocene Thermal Maximum or PETM is very important to understand because it indicates a very powerful, albeit brief, injection of carbon into the atmosphere that is akin to what is happening now,” said he declared.

Radiolarians

Examples of radiolarians, a type of microplankton. These tiny lifeforms need normal salinity seawater with plenty of nutrients, including silica, to grow and maintain their glassy shells. Researchers from the University of Texas Institute of Geophysics have found fossilized radiolarians in geological samples dating back 56 million years, proving that life persisted in the Gulf of Mexico despite global warming that has made many barren oceans. Credit: US Geological Survey

By examining a collection of mud, sand and limestone deposits located around the gulf, Cunningham and his colleagues looked at the prehistoric era of global warming and its effects on marine life and chemistry.

They dug up rock chips left over from oil and gas drilling and discovered a slew of microfossils of radiolarians, a species of plankton that had unexpectedly thrived in the Gulf during ancient global warming. They came to the conclusion that radiolarians and other microbes managed to thrive despite the more adverse effects of the Earth’s increasing climate thanks to a continuous supply of river sediments and circulating ocean waters.

“In many places the ocean was absolutely uninhabitable for anything,” said UTIG biostratigrapher Marcie Purkey Phillips. “But we just don’t seem to be seeing as severe of an effect in the Gulf of Mexico as what’s been seen elsewhere.”

The reasons for this are the geological forces that reshaped North America at the time. About 20 million years before ancient global warming, the rise of the Rocky Mountains had redirected rivers northwest from the Gulf of Mexico – a tectonic shift known as the Laramide uplift – sending much of the rivers from the mainland through what is now Texas and Louisiana into the deep waters of the Gulf.

Map of the Gulf of Mexico

A map of the Gulf of Mexico shows the rivers that flowed into the gulf 56 million years ago. The colored circles mark the location of the geological samples. The orange arrows mark the outlets of the rivers. The data was used in a study by the University of Texas Institute of Geophysics to investigate the climate impact of ancient global warming on the Gulf and its implications for energy reserves in the basin. Credit: University of Texas Institute of Geophysics

When global warming hit and North America became warmer and wetter, rain-filled rivers pumped nutrients and sediments into the basin, providing many nutrients for phytoplankton and other sources of food for radiolarians.

The results also confirm that the Gulf of Mexico remained connected to the Atlantic Ocean and that the salinity of its waters never reached extremes – a question that until now had remained open. According to Phillips, the mere presence of radiolarians – which only thrive in nutrient-rich water that is no saltier than seawater today – confirmed that the waters of the Gulf have not become too salty. Cunningham added that the organic content of the sediments decreased farther from the coast, a sign that deep currents driven by the Atlantic Ocean were sweeping the bottom of the basin.

The research accurately dates the closely related geological strata of the Wilcox Group (a set of rock layers that host a major petroleum system), a feat that can help find undiscovered oil and gas reserves in formations of the same age. At the same time, the findings are important for researchers studying the effects of current global warming, as they show how the Gulf’s water and ecology changed during a very similar period of climate change ago. long time.

The study compiled geological samples from 36 industrial wells scattered across the Gulf of Mexico, as well as a handful of scientific drilling expeditions, including the University of Texas at Austin’s 2016 impact survey. of the asteroid Chicxulub, which led to the extinction of non-avian dinosaurs. .

For John Snedden, study co-author and principal investigator at UTIG, the study is a perfect example of industry data being used to answer important scientific questions.

“The Gulf of Mexico is a tremendous natural archive of geological history that is also very closely studied,” he said. “We used this very robust database to look at one of the highest thermal events in the geological record, and I think it gave us a very nuanced view of a very important time in Earth’s history. .”

Snedden is also director of the University of Texas Gulf Basin Deposit Synthesis Program, an industry-funded project to map the geological history of the entire Gulf Basin, including ongoing research. UTIG is a research unit of the Jackson School of Geosciences at the University of Texas.

Reference: “Trends in productivity and organic carbon in the Wilcox Group in the Deep Gulf of Mexico: evidence for ventilation during the Paleocene-Eocene Thermal Maximum” by Robert Cunningham, Marcie Purkey Phillips, John W. Snedden, Ian O. Norton, Christopher M Lowery, Jon W. Virdell, Craig D. Barrie and Aaron Avery, April 8, 2022, Marine and petroleum geology.
DOI: 10.1016/j.marpetgeo.2022.105634

Teresa H. Sadler