Blog Archives

Scientists Conduct Expedition of Atlantis Massif in North Atlantic Ocean

image

Scientists recently concluded an expedition aboard the research vessel JOIDES Resolution to learn more about Atlantis Massif, an undersea mountain, or seamount, that formed in a very different way than the majority of the seafloor in the oceans.

Unlike volcanic seamounts, which are made of the basalt that’s typical of most of the seafloor, Atlantis Massif includes rock types that are usually only found much deeper in the ocean crust, such as gabbro and peridotite.

The expedition, known as Integrated Ocean Drilling Program (IODP) Expedition 340T, marks the first time the geophysical properties of gabbroic rocks have successfully been measured directly in place, rather than via remote techniques such as seismic surveying.

With these measurements in hand, scientists can now infer how these hard-to-reach rocks will “look” on future seismic surveys, making it easier to map out geophysical structures beneath the seafloor.

“This is exciting because it means that we may be able to use seismic survey data to infer the pattern of seawater circulation within the deeper crust,” says Donna Blackman of the Scripps Institution of Oceanography in La Jolla, Calif., co-chief scientist for Expedition 340T.

“This would be a key step for quantifying rates and volumes of chemical, possibly biological, exchange between the oceans and the crust.”

Atlantis Massif sits on the flank of an oceanic spreading center that runs down the middle of the Atlantic Ocean.

As the tectonic plates separate, new crust is formed at the spreading center and a combination of stretching, faulting and the intrusion of magma from below shape the new seafloor.

Periods of reduced magma supplied from the underlying mantle result in the development of long-lived, large faults. Deep portions of the crust shift upward along these faults and may be exposed at the seafloor.

This process results in the formation of an oceanic core complex, or OCC, and is similar to the processes that formed the Basin and Range province of the Southwest United States.

“Recent discoveries from scientific ocean drilling have underlined that the process of creating new oceanic crust at seafloor spreading centers is complex,” says Jamie Allan, IODP program director at the U.S. National Science Foundation (NSF), which co-funds the program.

“This work significantly adds to our ability to infer ocean crust structure and composition, including predicting how ocean crust has ‘aged’ in an area,” says Allan, “thereby giving us new tools for understanding ocean crust creation from Earth’s mantle.”

Atlantis Massif is a classic example of an oceanic core complex.

Because it’s relatively young–formed within the last million years–it’s an ideal place, scientists say, to study how the interplay between faulting, magmatism and seawater circulation influences the evolution of an OCC within the crust.

“Vast ocean basins cover most of the Earth, yet their crust is formed in a narrow zone,” says Blackman. “We’re studying that source zone to understand how rifting and magmatism work together to form a new plate.”

The JOIDES Resolution first visited Atlantis Massif about seven years ago; the science team on that expedition measured properties in gabbro.

But they focused on a shallower section, where pervasive seawater circulation had weathered the rock and changed its physical properties.

For the current expedition, the team did not drill new holes.

Rather, they lowered instruments into a deep existing hole drilled on a previous expedition, and made measurements from inside the hole.

The new measurements, at depths between 800 and 1,400 meters (about 2,600-4,600 feet) below the seafloor, include only a few narrow zones that had been altered by seawater circulation and/or by fault slip deformation.

The rest of the measurements focused on gabbroic rocks that have remained unaltered thus far.

The properties measured in the narrow zones of altered rock differ from the background properties measured in the unaltered gabbroic rocks.

The team found small differences in temperature next to two sub-seafloor faults, which suggests a slow percolation of seawater within those zones.

There were also significant differences in the speed at which seismic waves travel through the altered vs. unaltered zones.

“The expedition was a great opportunity to ground-truth our recent seismic analysis,” says Alistair Harding, also from the Scripps Institution of Oceanography and a co-chief scientist for Expedition 340T.

“It also provides vital baseline data for further seismic work aimed at understanding the formation and alteration of the massif.”

The Integrated Ocean Drilling Program (IODP) is an international research program dedicated to advancing scientific understanding of the Earth through drilling, coring and monitoring the subseafloor.

The JOIDES Resolution is a scientific research vessel managed by the U.S. Implementing Organization of IODP (USIO). Texas A&M University, Lamont-Doherty Earth Observatory of Columbia University and the Consortium for Ocean Leadership comprise the USIO.

Two lead agencies support the IODP: the U.S. National Science Foundation and Japan’s Ministry of Education, Culture, Sports, Science and Technology.

Additional program support comes from the European Consortium for Ocean Research Drilling, the Australia-New Zealand IODP Consortium, India’s Ministry of Earth Sciences, the People’s Republic of China’s Ministry of Science and Technology, and the Korea Institute of Geoscience and Mineral Resources.

Source

Map picture

Amount of Coldest Antarctic Water Near Ocean Floor Decreasing for Decades

image

Scientists have found a large reduction in the amount of the coldest deep ocean water, called Antarctic Bottom Water, all around the Southern Ocean using data collected from 1980 to 2011. These findings, in a study now online, will likely stimulate new research on the causes of this change.

Two oceanographers from NOAA and the University of Washington find that Antarctic Bottom Water has been disappearing at an average rate of about eight million metric tons per second over the past few decades, equivalent to about fifty times the average flow of the Mississippi River or about a quarter of the flow of the Gulf Stream in the Florida Straits.

“Because of its high density, Antarctic Bottom Water fills most of the deep ocean basins around the world, but we found that the amount of this water has been decreasing at a surprisingly fast rate over the last few decades,” said lead author Sarah Purkey, graduate student at the School of Oceanography at the University of Washington in Seattle, Wash. “In every oceanographic survey repeated around the Southern Ocean since about the 1980s, Antarctic Bottom Water has been shrinking at a similar mean rate, giving us confidence that this surprisingly large contraction is robust.”

Antarctic Bottom Water is formed in a few distinct locations around Antarctica, where seawater is cooled by the overlying air and made saltier by ice formation. The dense water then sinks to the sea floor and spreads northward, filling most of the deep ocean around the world as it slowly mixes with warmer waters above it.

The world’s deep ocean currents play a critical role in transporting heat and carbon around the planet, thus regulating our climate.

While previous studies have shown that the bottom water has been warming and freshening over the past few decades, these new results suggest that significantly less of this bottom water has been formed during that time than in previous decades.

“We are not sure if the rate of bottom water reduction we have found is part of a long-term trend or a cycle,” said co-author Gregory C. Johnson, Ph.D., an oceanographer at NOAA’s Pacific Marine Environmental Laboratory in Seattle. “We need to continue to measure the full depth of the oceans, including these deep ocean waters, to assess the role and significance that these reported changes and others like them play in the Earth’s climate.”

Changes in the temperature, salinity, dissolved oxygen, and dissolved carbon dioxide of this prominent water mass have important ramifications for Earth’s climate, including contributions to sea level rise and the rate of Earth’s heat uptake.

“People often focus on fluctuations of currents in the North Atlantic Ocean as an indicator of climate change, but the Southern Ocean has undergone some very large changes over the past few decades and also plays a large role in shaping our climate,” said Johnson.

The data used in this study are highly accurate temperature data repeated at roughly 10-year intervals by an international program of repeated ship-based oceanographic surveys. Within the U.S., the collection of these data has been a collaborative effort of governmental laboratory and university scientists, funded primarily by NOAA and the National Science Foundation. However, much of the data used in this study were measured by international colleagues.

“Collection of these data involves 12-hour days, seven days a week, of painstaking, repetitive work at sea, often for weeks on end with no sight of land. We are grateful for the hard work of all those who helped in this effort,” said Purkey.

Source

NOAA

Scientists Aboard Iberian Coast Ocean Drilling Expedition Report Early Findings

image

Mediterranean bottom currents and the sediment deposits they leave behind offer new insights into global climate change, the opening and closing of ocean circulation gateways and locations where hydrocarbon deposits may lie buried under the sea.

A team of 35 scientists from 14 countries recently returned from an expedition off the southwest coast of Iberia and the nearby Gulf of Cadiz. There the geologists collected core samples of sediments that contain a detailed record of the Mediterranean’s history. The scientists retrieved the samples by drilling into the ocean floor during an eight-week scientific expedition onboard the ship JOIDES Resolution.

The group–researchers participating in Integrated Ocean Drilling Program (IODP) Expedition 339: Mediterranean Outflow–is the first to retrieve sediment samples from deep below the seafloor in this region.

Much of the sediment in the cores is known as “contourite” because the currents that deposit it closely follow the contours of the ocean basin.

“The recovery of nearly four kilometers of contourite sediments deposited from deep underwater currents presents a superb opportunity to understand water flow from the Mediterranean Sea to the Atlantic Ocean,” says Jamie Allan, program director at the National Science Foundation (NSF), which co-funds IODP.

“Knowledge of this water flow is important for understanding Earth’s climate history in the last five million years.”

“We now have a much greater insight into the distinctive character of contourites, and have validated beyond doubt the existing paradigm for this type of sedimentation,” says Dorrik Stow of Heriot-Watt University in the United Kingdom and co-chief scientist for Expedition 339.

The world’s oceans are far from static. Large currents flow at various depths beneath the surface. These currents form a global conveyor belt that transfers heat energy and helps buffer Earth’s climate.

Critical gateways in the oceans affect circulation of these major currents.

The Strait of Gibraltar is one such gateway. It re-opened less than six million years ago.

Today, deep below the surface, there is a powerful cascade of Mediterranean water spilling out through the strait into the Atlantic Ocean.

Because this water is saltier than the Atlantic–and therefore heavier–it plunges more than 1,000 meters downslope, scouring the rocky seafloor, carving deep-sea canyons and building up mountains of mud on a little-known submarine landscape.

The sediments hold a record of climate change and tectonic activity that spans much of the past 5.3 million years.

The team found evidence for a “tectonic pulse” at the junction between the African and European tectonic plates, which is responsible for the rising and falling of key structures in and around the gateway.

This event 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.

“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 Javier Hernandez-Molina of the University of Vigo in Spain and co-chief scientist for Expedition 339. “We now have that understanding and a record of a deep, powerful Mediterranean outflow through the Gibraltar gateway.”

The first drill site, located on the west Portuguese margin, provided the most complete marine sediment record of climate change over the past 1.5 million years of Earth history.

The sediment cores cover at least four major ice ages and contain a new marine archive to compare against ice core records from Greenland and Antarctica, among other land-based records.

The team was surprised to find exactly the same climate signal in the mountains of contourite mud they drilled in the Gulf of Cádiz.

Because these muds were deposited much 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,” Hernandez-Molina says.

“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 contourite sediments.”

The team also found more sand among the contourite sediments than 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 kilometers from the Gibraltar gateway.

All testify to the strength, velocity and duration of the Mediterranean bottom currents. The finding could affect future oil and gas exploration, the researchers believe.

“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 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,” says Stow. “Our findings could herald a significant shift in future exploration targets.”

IODP is an international research program dedicated to advancing scientific understanding of the Earth through drilling, coring, and monitoring the subseafloor.

IODP is supported by two lead agencies: the U.S. National Science Foundation and Japan’s Ministry of Education, Culture, Sports, Science, and Technology. Additional program support comes from the European Consortium for Ocean Research Drilling, the Australia-New Zealand IODP Consortium, India’s Ministry of Earth Sciences, the People’s Republic of China (Ministry of Science and Technology), and the Korea Institute of Geoscience and Mineral Resources.

The JOIDES Resolution is a scientific research vessel managed by the U.S. Implementing Organization of IODP (USIO). Texas A&M University, Lamont-Doherty Earth Observatory of Columbia University, and the Consortium for Ocean Leadership comprise the USIO.

Related articles

Source

USA: Keppel to Turn Ocean Voyager into Ocean Onyx

image

Keppel AmFELS, a shipyard strategically located at the gateway of the Gulf of Mexico, Brownswille, Texas has secured a contract from Diamond Offshore to construct and upgrade a moored semisubmersible rig with delivery scheduled for 3Q 2013. The estimated shipyard contract price is approximately US$150 million.

The rig, to be named Ocean Onyx, will be constructed from an existing hull from a Diamond Offshore cold stacked unit, which previously operated as the Ocean Voyager.

Keppel AmFELS’ scope of work on the Ocean Onyx includes the reconstruction of the rig, installation of advanced equipment such as a modern drilling package, and installation of sponsons to the pontoons to enhance the stability of the rig in deepwater. The rig will be designed to operate in water depths of up to 6,000 feet and will have a variable deck load of 5,000 long tonnes, a five-ram blowout preventer, and quarters capacity for 140 personnel.

Mr Larry Dickerson, President and CEO of Diamond Offshore, said, “We have worked with Keppel for more than a decade, and our rigs have consistently been delivered on time and within budget, whether in the US or Singapore. With Keppel’s track record as a leading offshore yard, we are confident that this project will also be a success.”

Keppel O&M has previously built four similar semisubmersible rigs for Diamond Offshore: the Ocean Baroness, Ocean Rover, Ocean Endeavour and Ocean Monarch.

Mr Tan Geok Seng, President of Keppel AmFELS, said, “We are pleased to be able to embark on another major rig project for Diamond Offshore, who has worked with Keppel on more than 20 projects since 1996. Diamond’s rigs are sent regularly to our yards around the world for maintenance, repair and upgrade, and Keppel AmFELS has proven to be their choice yard in the US Gulf of Mexico. Having built a long-term partnership with Diamond, we understand the company’s needs and are confident of delivering another high quality rig to their satisfaction.”

Articles

Source

Ocean Rig Bidding to Rent 5 Drillships to Petrobras, Brazil

image

DryShips Inc confirmed market speculation that its Ocean Rig UDW drilling unit was bidding to rent out five new drillships to Brazilian state oil company, Petrobras .

Shares of Athens-based DryShips were up 9 percent at $2.95 on Tuesday morning on Nasdaq, a day after it posted estimate-beating third-quarter profit.

Through its majority-owned Ocean Rig unit, DryShips owns and operates 9 ultra-deepwater drilling units, comprising 2 ultra-deepwater semisubmersible rigs and 7 ultra-deepwater drillships.

“We are a part of the tender process for the Petrobras domestic tender. The contracts are still being negotiated, it’s still at a very early stage,” Chief Operating Officer Pankaj Khanna said on a conference call.

He said the 15-year contract at a rate of $620,000 per day would be “very profitable,” adding that the company was confident of receiving financing for 85 to 90 percent of the transaction.

“It would be really positive for earnings in the future, especially given that the current rates are at $500,000 per day for a one-year contract,” analyst Salvatore Vital of Sterne, Agee & Leach told Reuters.

Earlier in the year Ocean Rig, which started trading on Nasdaq on October 6, won a $1.1 billion deepwater drilling contract from Brazil’s Petrobras.

Source: Reuters

Source

%d bloggers like this: