On station

At about 6 am yesterday, we reached our first station! We recovered a sediment trap that had been deployed during a previous cruise, so now we have a nice picture of organic matter input to the seafloor over the course of a year. The majority of the food that arrives at the seafloor falls from shallower depth - dead animals, fecal pellets, dead plankton, discarded mucus. It sounds absolutely disgusting, but that's the menu for deep-sea benthos. In order to understand how much and what kinds of organic matter are supplied to the seafloor, we have to intercept and catch it, so we deploy sediment traps. 

The sediment trap

A sediment trap is essentially a giant funnel. It has a grate over the opening to filter out large objects that could clog it, and at the bottom, it narrows to a sample bottle. The sample bottles are held on a rotating platform and switch out throughout the year, so you can see how much organic material is deposited at the seafloor during different seasons. 

To deploy a sediment trap, you usually have to attach it to a mooring. Basically, you hook it onto a line, put a weight at the bottom and a float at the top. The weight ensures that the trap sinks and stays in place, while the float makes sure that it stays upright in the water column. In order to get the mooring back, you have to release the weight and allow the float to bring it back up to the surface. Releasing the weight is accomplished by an acoustic release, which is a link between the weight and the rest of the mooring that can receive acoustic signals. We send an acoustic signal from the ship; the acoustic release receives the signal, and the weight is released. Make sense? 

Oliver with one of the sediment trap
sample bottles.

The cool part about acoustic releases is that sometimes you can hear the signal from inside the ship. I remember lying in my bunk during a cruise last year and hearing a series of beeps out of nowhere. I eventually figured out the the beeps were the sound waves sent by a transponder on the ship to the acoustic release. The sound waves were sent through the water, but I could also hear them through the hull of the ship. 

Once we got the sediment trap back, all the sample bottles had to be removed from it. They already contained a fixative to preserve the samples, but we had to put in fresh fixative, seal the bottles, and store them for transport. I helped two others on board with this process. The samples will be sorted and quantified back on land. In case you're wondering, yes, that means someone will be responsible for sorting poop from dead plankton. I've been told you can use the shape of a fecal pellet to identify what species it came from (cool, right?). 

It's nice to have our first station done. On to the next!