The Good, the Bad and the Ugly in the world of ocean sediment coring...

July 16, 2010

Location: Mid-Atlantic

Coordinates Lat / Lon: 36* 39.0991'N/ 46*11.1667' W
Air Temp: 25.60*C / 78.08*F
Humidity: 82%
Sea Surface Temp (SST): 25.84*C / 78.51*F
Salinity: 35.96 psu
Depth: 4985 m / 4.985 km / 3.097 miles

Our two-day transit has ended and the team started with a gravity core.

"We'll be flirting with 5000m, " says coring and dredging specialist Chris Moser. Very cool! Chris says this core will take about four hours because this water is so

The plan was NOT to do a long core today but the gravity core came back so beautifully that they're going for it! It will take hours to reach the bottom and to return. After it is pulled up and processed, the multicore will go down. The team is in for a late night!

Let's talk about the long core:
After the long core is brought to the surface and onto to the boat the team jumps into action.

The long core components are enormous. Bob White and Frank Scofield
are pictured here in the "man basket" located at the
stern of the R/V Knorr. It swings around from
stern to side to allow people to access the long core for the "extruding process". This link shows a picture of Cheryl Manning of Evergreen High School, Colorado working in the man basket. She is currently a teacher of Earth and Environmental Science and she sailed on the R/V Knorr for the Armada Project in the winter of 2009.

People in the man basket are located at the top of the core and they send plastic "bullets" down the core shaft that result in the extrusion of (hopefully) mud-filled segments of PVC from the bottom of the core. At the tip of the core, the sharp core cutter and the core catcher are removed. To the right WHOI lead mechanic Jeff Hood is cutting the PVC into manageable lengths as it is extruded.

A limitation of this technology is that if the sediment is too watery, the core catcher doesn't capture it. The sediment with the most water is the top section of the seafloor, where the ocean water meets the ocean floor. The long core can miss meters of top sediment. The average rate of deposition in the North Atlantic is 3-4 cm/1000 years. Keigwin believes that the rates of deposition for the sites he has selected to sample are possible 2-3 times higher than the average.

So what? This is important to know because missing a few meters of sediment in the core means that you're missing thousands of years of ocean history.

Ideally a core has effectively sampled the subsurface of the ocean floor. To the right there's a image of a fairly desirable core. This sediment is thick and continuous.

This image to the left shows a dreaded sight.

Look carefully at the open end of the PVC. Sediment laden water is pouring out from the long corer. We could be either losing thousands of years of ocean floor history or ending up with a disrupted sequence of sediments. As the core is pulled out, suction can cause water to flow in between layers.

This (left) is the extremely sharp core cutter - it came up bent the other day! What did it? People speculated and it's entirely possible that when they cut the core open back at WHOI they'll find the culprit but they may not. One of Jeff's many skills is reshaping this custom cutter!

The picture at the top of the blog shows Sarah Schulenberg holding a mangled core catcher that was just pulled out of a long core. Jim Broda will work his magic to get that catcher back and ready for more!

The combination of "decision making on the fly" and the reality of utilizing a tool for which there really are no "stock" parts, reminds me of our Space Program. This team of scientists is working on a project with its own remarkable challenges and it takes talent and ingenuity to rise to meet it!

No comments:

Post a Comment