Monday, March 7, 2016

Dispatch From A Drilling (Coring) Ship

It's easy to forget one is on a ship aboard The JOIDES Resolution (named after Captain Cook's ship, she has crisscrossed the world's oceans in a manner befitting the name). The accommodations are bordering on luxurious, and most days the motion of the ship is hardly noticeable. Launched in 1978 with a major refit in 2007-2008 she is 143 meters long. Currently there are 125 people on board (now 124 after a medivac). It is like a floating city.
JOIDES Resolution, aka "JR" coming into Port Louis, Mauritius
The rig can drill in a water depth of ca 8000 m and then another 2000 m below the seafloor. On this expedition we have drilled in around 3000 meters depth and collected cores down to ca 300 meters below the sea floor. Carrying, cutting, and archiving sections of cores all day (which is mostly what I do), one can lose sight of the bigger picture. The sediments we are collecting were deposited up to 7 million years ago and tell the story of past climates. Paleontologists identify fossilized remains of benthic and planktonic foraminefera, diatoms, and radiolaria. Other specialists measure the the magnetism in the cores (the polarity of the earth's magnetic field has flipped many times in the earth's history). Combined with gamma ray emission, gamma ray transmission (measuring density), and other techniques these data allow scientist to date each section of sediment. Once the cores' ages are determined more detailed measurements are used to reconstruct the climate. The purpose of this expedition is to study the past behavior of The Agulhas Current and its influence on the climate (see this BBC blurb). As I write this, we are steaming north in The Mozambique Channel (between Mozambique and Madagascar) towards our next coring site.

The coring machinery includes a hollow steel tube (called the drill string) that is lowered to the ocean floor. This so-called drill string is assembled from 30 meter long sections and is fitted with a drill bit. Inside the drill string a ca 10 meter steel tube called the core barrel fitted with a plastic liner (the core liner, made from cellulose acetate butyrate), is lowered on a steel cable until it reaches the bottom of the drill string (which at the beginning of the drilling process should be hanging a couple of meters above the sea floor. The assembly is then pressurized with water (or mud) until two shear pins break, firing the core barrel into the ocean floor. The drill string then drills down around the core barrel until reaches the end.  The core barrel is then pulled up through the drill string onto the ship. The drilling crew immediately begin lowering another core barrel down the drill string as the core liner containing the core sample is pulled from the core barrel and handed over to the IODP technicians (of whom I am one). We cut the core liner with core inside into 1.5 meter sections which are immediately fed through three automated tracks with analytical instruments that measure among other things gamma ray transmission (density) and gamma ray emission. The core sections are then split lengthwise. One half becomes the archive section which is later sent to a core repository. The other half (the working half) is then studied further on the ship. As all this is happening another section of core is on its way up the drill string and we do it all again.

Check out for more information and for photos from this cruise.

A few more photos here.

14/04/16--I just came across co-chief scientist Sidney Hemming's blog from the cruise. She obviously has a much better idea what's going on that me:

And this map shows the ship's circuitous track during the expedition (ask my why the track looks like it does):