Monday, May 16, 2011

Sediment sampling: the business of collecting mud and sand

14th May 2011

Collecting mud… can’t be that hard, can it? Over the past couple of days, we have been trying various ways of collecting sediments from Burdwood Bank. We tried box coring first: this is when a big metal box is winched down to the seafloor and into the sediments, where large jaws are triggered to close and trap whatever mud and sands are in the box. Unfortunately, these didn’t work here – perhaps it was the wrong type of sediment, or perhaps the seas were too rough. Our next tactic was to use a kasten core – this is a long metal box, weighted down heavily, that is sunk into the seafloor and winched up, hopefully bringing with it a long column of sediment. This time we were more successful, retrieving about a foot of sediment containing sands and corals.

Kais Mohamed Falcon is the scientist on board heading up the sediment collection efforts….

“Obtaining sea-floor sediments from hundreds or thousands of meters deep is a tricky job. The sediment type has to be right so the sampling device, or corer, we are using does the job. Mud usually is easier to sample since the corer penetrates easily into it. Sandy and gravelly sediments usually are more difficult to obtain, because the corer usually gets stopped a few centimeters into it. Imagine pushing a tube through wet sand…you probably wouldn’t go further than a 4 or 5 centimeters, whereas in mud you probably would go all the way through it.

In addition to the sediment type, from which we normally have information provided by previous expeditions, nautical charts or just intuition based on the bottom topography, many other factors influence the outcome of each coring attempt. Unsteady seas pulling from the wire and unbalancing the corer, arrival of the corer at an angle with the bottom or just hitting a rock can ruin a coring attempt. It’s like trying to hit the sidewalk pavement with a long straw from the top of the Empire State Building with your eyes closed…you could easily hit the road, a car, people or a parking meter”

“When the corer comes back on board, there is always excitement on deck. Has the corer been damaged jeopardizing future coring attempts?, has it been successful in obtaining sediment?, how much sediment has been recovered?, what is in it?, how old it is?...this is the moment when exciting science begins!”

And now we’re off in transit again, heading towards the Shackleton Fracture Zone.

By: Kate and Kais

Weather: 38°F, windchill 22°F, wind 5-10 knots, foggy

Sampling from the Nathaniel B Palmer on a beautiful sunny day in the Southern Ocean (D. Case).

The marine techs deploying the box core. The box, mounted on a yellow frame, sinks into the sediment, where jaws are triggered to shut and trap sediment inside (R. waller).

The contents of the kasten core, recovered a few days ago (K. Falcon).

Geologist Kais taking some time to take some photos of the scenery (A. Margolin).

A misty morning view from the Palmer (S. Jennions).

1 comment:

  1. Alright! Now this is science! Weird to see the box core on a yellow frame ;)