Core samples from near the Strait of Gibraltar show the climate has shifted since about six million years ago. The work also provides new evidence of a deep-earth tectonic pulse in the region, according to researchers.
Working on board the research vessel JOIDES Resolution, the team took core samples near the Strait of Gibraltar off the coast of Spain and Portugal.
They examined the sedimentary record produced by strong ocean currents commonly called MOW (Mediterranean outflow water) through the Gibraltar gateway.
“Because the water is saltier than the Atlantic, and therefore heavier, it plunges more than 3,000 feet downslope, carving deep-sea channels, and building up mountains of mud on these underwater landscapes,” explains Carlos Alvarez Zarikian, a staff scientist of the International Ocean Discovery Program (IODP) headquartered at Texas A&M University.
“These sediments are called contourites because the currents that deposit them closely follow the contours of the ocean basin. They show various shifts of climate change over millions of years.”
Zarikian says the team set out to understand how the Strait of Gibraltar acted first as barrier, but later as a gateway over the past six million years as the MOW currents passed through area.
Further analysis of the contourites showed that they contained far more sand than expected.
“This vast sand sheet that extends about 60 miles from the Gibraltar gateway testifies to the strength and velocity of these Mediterranean currents,” Zarikian adds.
“We believe that these MOW currents initially entered the Atlantic Ocean as a weak circulation following the opening of the Strait of Gibraltar, and developed into more voluminous flows that influenced global circulation by the late Pliocene era.
“The findings show that there is a relationship between the climatic shifts and plate tectonic events, and they relate to overall plate reorganization over the North Atlantic. The oceans and climate are remarkably linked.”
The National Science Foundation funded the expedition project, which the Integrated Ocean Drilling Program–US Implementing Organization implemented. European grants and the Continental Margins Research Group at Royal Holloway University of London partially funded the study, which appears in Science.
《Onset of Mediterranean outflow into the North Atlantic》, Published on Journal 《Science》in June 2014.