JC114 in pictures and numbers

A flock of pelicans flying past the ship whilst at anchor in the Gulf of Panama with a fantastic view of Panama City and the Sonne.

The Cook has just sailed under the Bridge of the Americas and safely docked in Balboa, drawing to a close three hugely successful cruises for the OSCAR project.

 

A view over the aft deck on the last day of seismic activities, showing the streamer, the airguns in the water, and the magnetometer cable on the far right

On JC114 alone we've built up some impressive statistics, with:

5280 nautical miles sailed,

83 OBS's deployed and recovered (plus two vertical arrays),

95,500 airguns shots fired,

11 billion cubic inches of air pumped through our airguns,

1830 swath files processed,

80 (at least) red-footed boobies adorning the ship at one time,

234 whales and dolphins sighted, and

2 sea creatures boarding the ship via OBSs (a starfish and a crab) .

For the whole project we've completed three cruises on two ships for a total of 112 days at sea, and are incredibly grateful for the help we've received from all the scientists, technicians, crew and captains on board the James Cook and Sonne.

 

A OBS surfing the waves before recovery.

Although it's sad that the cruise has come to an end- this is just the beginning, as soon we'll be heading back to our respective institutions to begin analysing our fantastic data! 

 

A local fishing boat that brought us two huge dorado in exchange for our technicians fixing their bilge pump.

Finally, a thank you to our cruise blog contributors:

Gavin Haughton, Matt Funnell, Jowan Barnes, Richard Hobbs, Rob Harris, Christine Peirce, Dean Wilson, Emma Gregory and all contibutors of photographs.

 

Scientists on the bridge trying to spot the tailbuoy at the end of the streamer, 4.5 km behind the ship.

Thank you all for reading, we hope you've enjoyed hearing about our science at sea!

Two boobies perching on the A-frame with the Sonne in the background.

504B

By Richard Hobbs, OSCAR PI

Most scientists that study the ocean crust will have heard of the 504B. I heard about the site during my PhD when on a 6-month visit to Lamont-Doherty Earth Observatory, as it is now called, a research institute just north of New York in the United States. The drilling at site 504B started during my first Post-doctoral post as part of the British Institutions Reflection Profiling Syndicate in Cambridge, and here I am at the twilight of my career doing a geophysical survey over site 504B. 

So what is 504B? 504B is one of the deepest borehole ever drilled into ocean-crust and it is situated in the Panama Basin where we are working. The hole was started in 1988 as part of Leg-111 of the Ocean Drilling Project (ODP), an internationally funded project to explore the deep ocean by direct sampling. Before ODP, and its forerunner DSDP, most people that studied ocean crust worked on ophiolites – deformed fragments of ocean crust that have been pushed up to the surface by tectonic forces. The drill ship, JOIDES Resolution, was capable of sampling rocks under the oceans in water depths of over 8000 m so it was now possible to sample ocean rocks in-situ and answer first-order questions about their age, composition, and properties of the ocean crust. One of the holes, 504B, was selected as the site to attempt to drill to the level at which the ocean-crust had originally formed at the axial magma chamber. The site is 230 km south of the present-day ridge axis and drilled into crust that is 5.9 Ma (million years old). The hole reached a depth of 2111 m below the ocean floor over a series of expeditions from 1986, with two in 1991 and the last in 1993.

Cartoon of well 504B, showing the crustal structure (after Carlson 2011).

So why is 504B important to the OSCAR project? From a geophysical perspective, I use remote sensing to learn about the earth on which we live. Some of these methods have been explained in previous posts. Though I can map the physical properties to the Earth, I need calibration points like 504B so I my measurements can be directly related to actual rock. Also, this hole provides important evidence of alteration of the basalt rocks by the passage of high-temperature hydrothermal fluids shortly after its formation some 5.9 million years ago. In fact there is still some residual water circulation in the cracks and fractures at this present-day even though the ocean crust is now sealed from the ocean by over 250 m of sediment that acts like a lid.

Determining the thickness of this sediment 'lid' is a major objective for the OSCAR project as this  controls the type of heatflow from the crust into the ocean. The best method to remotely map the thickness of layers of sedimentary rock is seismic reflection. An acoustic pulse is generated by a sound source behind the vessel. When the pulse reaches the sea-bed a fraction of the energy is reflected back to the surface, the rest continues to propagate deeper into the Earth and at every deeper change in the sediment generates another reflected echo. At the surface we tow an array of highly sensitive hydrophone detectors that record the returning echoes which we can turn in to pictures that give a cross-section through the sediments.

Seismic reflection section of the crust at hole 504B, showing the sediment layers in high resolution overlaying the ocean crust