Coring Calamities

The marine technicians steady the Kasten corer after its return to the surface.

We are still at yesterday’s sampling site this morning, waiting for a piece of coring equipment, called a Kasten corer, to return from the seafloor. You may have read about our previous efforts using the megacorer. We’ve had little success with the megacorer at this current location, due to the nature of the mud on the seafloor below us. Some members of the science team have been up basically all night, catching a couple of hours sleep here and there perhaps, as they repeatedly wait for equipment return to the surface—but without the sediment we need. Working through the night is not unusual, except that our efforts have been mostly thwarted in this location; we had expected to be on our way to the next site by now. But coring, as I am discovering, is a very tricky business.

The Kasten corer is a single corer, so although it is not heavier than the megacorer, all the force is in one place. So, we are hoping it will push into the dense mud we’re encountering. Interestingly, the diatoms we are seeking are causing the problems; they make a sort of mesh that is difficult to penetrate.

The Kasten corer is topped with lead plates to make it heavy; more plates can be added to increase its weight when needed.

There is no guarantee of success during coring. We send a large piece of equipment into the dark depths of the ocean—today 2800+ meters (about 1.7 miles) beneath the ship, though at other sites, it has been even deeper. There’s no way of us seeing what’s happening down there. We must rely on a monitor that shows us the tension on the cable that lowers the coring equipment, as well as on our knowledge of the seafloor obtained during our initial survey.

We have a series of monitors that provide all sorts of information such as the depth and profile of the seafloor, the wind strength and direction, the payout of cables lowering equipment, and much more. One also provides views of the ship, so we can see what is happening during an operation. (Can you find the monitor that shows us the depth of the ocean here is 2,805 meters?)

As the equipment descends, the tension on the cable gradually increases due to the weight of the wire as it descends deeper into the ocean.

We watch for a sudden drop-off in the tension around the known depth of the seafloor, which indicates that the equipment has touched down, therefore taking tension off the cable. There is a pause as we wait for the coring device to sink into the mud.

Can you see where the tension on the line suddenly drops?

Then the winch operator puts the winch in reverse. There is a sudden increase in the tension on the cable as it picks up the corer, which is hopefully now heavier due to the mud it has retrieved. As the equipment makes its way back to the surface, the tension on the cable gradually decreases.

Throughout this process, the ship can be rolling and pitching on the surface waves in the rough Antarctic Circumpolar Current, placing irregular and unpredictable tension on the cable. This is, after all, the region long-known by sailors as the Screaming Sixties and some of the roughest seas on our planet. This can have a negative effect on the coring equipment. Unfortunately, we have experienced this on more than one occasion where some mud was—we believe—washed out of the coring tubes due to the water’s turbulent action, leaving us with less sediment that we had hoped.

Also, until the coring equipment returns to the surface, we can’t see whether, despite our careful survey efforts prior to its deployment, it has landed exactly on an area with mud. After all, the diameter of these coring devices is relatively small, and it might make contact with an area that is rock or sand, even though mud might be right nearby. This adds to the unpredictable and sometimes frustrating nature of coring.

And indeed, when we open it up, unfortunately, this Kastencore contains only a small amount of sediment. Some of the team liken its consistency to an athletics mat: springy enough to bounce a heavy Kasten corer off it.

As Becky said to me the other day, “Well, there’s a lot of hubris in us sending these pieces of equipment to the bottom of the ocean and expecting them to come back.” But we persist and repeat our coring efforts, using a device such as the Kasten corer when needed and adding even more weight. We know there is diatom-rich mud deep below us, but getting the equipment available to us to successfully penetrate it is key. The small amounts of sediment we have recovered from this site so far have shown us that the seafloor here has exactly the kind of diatom fossil-rich mud we are seeking—it’s just a matter of us getting it successfully to the surface.