Heriot-Watt scientist leads research adventure into six million years of earth history

In an underwater river of sand and mud off the Iberian Coast, a scientist from Heriot-Watt University has discovered new evidence buried under six million years of earth history, which has significantly advanced our understanding of climate change.

Professor Dorrik Stow, Director of Research at the Institute of Petroleum Engineering at Heriot-Watt University, is leading an international team of 35 top researchers from 14 countries on an eight-week, sea-based scientific drilling expedition to investigate the earth's contours and currents and to collect sediment samples from deep below the seafloor, off the southwest coast of Iberia.

The Integrated Ocean Drilling Program (IODP) Expedition 339: Mediterranean Outflow has already been heralded a major success following the team's discovery of new evidence of a deep-earth tectonic pulse and the retrieval of a detailed record of climate changes as a result of drilling down more than five kilometres into the earth's core.

Findings

At a conference being held today (January 18, 2012) in Lisbon, Portugal, Professor Stow will present the team's findings. These will include:

Evidence of a powerful cascade of Mediterranean water spilling out through the Strait into the Atlantic Ocean

As this water is saltier than the Atlantic - and therefore heavier - it plunges more than 1000 metres down slope, scouring the rocky seafloor, carving deep-sea canyons and building up mountains of mud on a little known submarine landscape. These sediments hold a record of climate change and tectonic activity that spans much of the past 6 million years.

The first record of just when this deep Mediterranean undercurrent began to flow soon after the opening of the Strait of Gibraltar

Critical gateways such as this influence the passage of major currents around the world's oceans, which form a global conveyer belt that transfers heat energy and helps buffer Earth's climate from the extremes.

New & unexpected evidence

"We set out to understand how the Strait of Gibraltar acted first as a barrier and then a gateway over the past six million years," says Dorrik Stow. "We now have that understanding and a record of a deep, powerful Mediterranean Outflow through the Gibraltar gateway.

But, in addition to many eagerly anticipated answers to their questions, " €¦the expedition brought us some wholly unexpected scientific results." he adds.

The team found new and unexpected evidence for a "tectonic pulse" at the junction between the African and European tectonic plates, which is responsible for causing a repeated rising and falling of key structures in and around the gateway. It also led to strong earthquakes and tsunamis that dumped large flows of debris and sand into the deep sea. At four of the seven drill sites, there was also a major chunk of the geologic record missing from the sediment cores - evidence of a strong current that scoured the seafloor.

Historical  record of climate change

The first drill site, located on the west Portuguese margin, was chosen to provide the most complete marine sediment record of climate change through the past 1.5 million years of Earth history. These cores cover at least four major ice ages, and provide a new marine archive to compare against ice core records from Greenland and Antarctica, among other land-based records.

But the team was surprised to find exactly the same climate signal in the mountains of contourite mud they drilled in the Gulf of Cádiz. Moreover, because these muds were deposited many times faster than the sediments at the Portuguese margin site, the record from these cores could prove to yield even richer, more detailed climate information.

"Cracking the climate code will be more difficult for contourites because they receive a mixed assortment of sediment from varying sources," explains Javier Hernandez-Molina, from the University of Vigo in Spain, Co-Chief Scientist with Dorrik Stow. "But the potential story that unfolds may be even more significant. The oceans and climate are inextricably linked. It seems there is an irrepressible signal of this nexus in the contourite sediments we have drilled."

Potential for carbon storage

In another surprising turn, the team found a great deal more sand among the contourite sediments than anyone had expected. The scientists found this sand filling the contourite channels, deposited as thick layers within mountains of mud, and in a single, vast sand sheet that spreads out nearly 100 kilometres from the Gibraltar gateway. All testify to the great strength, high velocity and long duration of the Mediterranean bottom currents. Moreover, the find could impact future oil and gas exploration.

"The thickness, extent and properties of these sands make them an ideal target, in places where they are buried deeply enough to allow for the trapping of hydrocarbons," Stow explains. The sands are deposited in a completely different manner, in channels and terraces cut by bottom currents; in contrast, typical reservoirs form in sediments deposited by downslope "turbidity" currents. "The sand is especially clean and well sorted, and therefore very porous and permeable. Our findings could herald a significant shift in future exploration targets."