October 4, 2012
All We Need Is Mud
|Close-up of multicore tube |
with brownish-red mud
Mud, mud, mud. Core after core we bring it on board, slice it up, preserve it, wash down the equipment and get ready for more. When we aren’t processing mud, we are labeling jars to store the mud until we look at it under the microscope back home. When we’re not doing that, we are spending time figuring out which site to get mud from next! The more mud you have the better.
|Recovering box core - note the muddy water.|
On this leg of the cruise we were hoping to sample a couple of sites that were sampled about 10 years ago. These provide some of the only sites that have baseline data pre-oil spill for the sediment macrofauna community. Macrofauna are tiny animals from a variety of phyla, generally between 300um-1mm in size. Macrofauna are one of the key groups that mix the sediments – a process called bioturbation. To be able to have comparable samples to the previous study, we had to use a piece of equipment called a box core. The box core takes a large square of mud 0.5m on a side. The ship had one on board, but had not used it before. We decided to test it out first to get an idea of how long processing samples from it would take. So we went ot the first of the sites in deSoto canyon where previous sampling had been done. The trick to using a box core is to get it deep enough into the mud that the weight of water on top of the mud in the box does not wash all the mud out during recovery. We deployed the box core once – not much luck – it came up with muddy water pouring out the sides. At least we got some mud, but it was all stirred up inside and slumped over. We decided to add some weights for the box core would go deeper and tried again. Again it came up with muddy water pouring out. It had gone deeper, but still not deeper enough.
|View inside a box core.|
We tried one last round with still more weights. There was excitement as the core came on deck without any muddy water coming out. But when we got the box open and siphoned off the overlying water, it was clear this was not a good core either. We decided to process the sample so we would have something from the site. Wow did that take a long time! A core .5m on a side is .25m2 of mud x 1 cm deep for the first layer, 4 cm deep for the second layer and 5 cm deep for the final layer. 1.25m3 of mud takes a looooooooong time to sieve!
|Multicore on deck|
We moved onto our next site and back to the old reliable multicore. Still takes some time to process, but a lot less of it. At our first site, called XC-3, we found something interesting, mud which was a funny brownish red color. I hadn’t seen mud quite this color before, although this is my first time sampling in the Gulf of Mexico, I had worked in the Atlantic, North and South Pacific and Antarctic on deep-sea mud. It usually light brown to gray, sometimes greenish. The mud appears layered – with a top layer usually a few cm deep a different color than the mud below. In this case the reddish-brown mud was a high contrast to the light gray mud beneath it. Other sites we have been to since that site did not have the same color mud.
Full cores on multicorer
Lots of worms and lots of burrows. One neat thing with multicores is the sediment surface is often preserved very nicely, you can see tubes and burrows just the same as they look on the seafloor. We hit one of these borrow dead-center with a multicore tube at our third site. We dug down deep in the core to try to find the owner, but they weren’t home. Their burrow helped mix sediment from the surface all the way down to over 15cm deep in the core though! On another core, there was also a burrow, but since the first one was empty, we didn’t dig deeper into the core once we got our samples. As Kayla was washing out the core tube, she found a really neat cactus worm (see below) that was home in that burrow! It almost washed overboard, but we picked it up off the deck for a picture. It is probably a molpadiid, one of the families of sea cucumbers that make burrows in deep-sea mud. We found a smaller one that looked very similar in another core later at the same site.
Cactus worm (priapulid) from burrow in core.
We’ve also found a few interesting large polychaetes. Unfortunately our scope camera isn’t working right, but we will try to get some images of these for you as the cruise progresses.
Just about time for more mud!
|Dr. Amy Baco-Taylor|
Florida State University