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Emily Davenport's picture

Depth: 50 meters

Well, I will reveal the mystery of the cups, as I don't want to keep everyone in suspense TOO long! Due to the amount of air in Styrofoam and the pressure of the water, the cups shrink to a miniature version of themselves. These cups started out at about 12 ounces- think of a *grande *sized cup at Starbucks- and ended up being only a couple ounces. The cool part is that everything shrinks- so all the decorations we put on them shrink as well. It's pretty neat to see!

I'd like to talk a little bit more about what our team does on the Healy, and why we are here in the Bering Sea. For those of you that read my journals last year, this may be a bit of a repeat.

At every station there is a sampling plan- we have many instruments that need to be deployed on the ship at every station, and they cannot be deployed simultaneously- meaning that things like CTD and multi-corer cannot go into the water at the same time. This is mainly for safety- so that they don't get tangled up underneath the ship, because the ship drifts with the water current even while we are stopped. Sometimes at stations they send out a team onto the ice which can take 6-8 hours, or the helicopter goes out for awhile, and we can't be on the deck when the helicopter leaves or comes back (again for safety). Stations can often take several hours, depending on the amount of stuff that needs to go on at each station. Once the plan is decided, there is a specific time for each instrument to be deployed. On our end, this means that we core the sediment at a specific time- which could be at any time of the day, depending on when we get to the station. We are lucky enough to have a technician that gets the corer ready for us- this is Paul Walczak from Oregon State University. Oregon State University owns this piece of equipment, and sends it on various cruises, along with a technician. Paul works really hard to make sure that the corer is in proper working order and ready to go when we're on station. He also keeps a log for each station- including latitude, longitude, station depth, etc.

Paul WalczakPaul and the multicorer on Healy- another day at work for those two!

After the multicorer comes up, we look at the cores that came up with it to make sure they are good. A good core is a core tube full of mud, with the overlying water clean and clear, not murky. A bad core is a core tube with very little (or no) mud and cloudy overlying water.

Bad coresThe multicorer with a bad set of cores (see all that murky water and not much mud)

Sediment CoresCore tubes with a good set of cores (nice clear water and lots of mud!)

The next thing we do is take a look at all the cores and decide what core goes to what experiment. We have several things we test at each station: radon (a gas that naturally occurs in the sediments), nutrients in the sediments, oxygen in the sediments, and animals in the sediments. Ideally we would love to see 16 beautiful cores come off of the multicorer- this means 2 drops of the corer at each station with 8 core tubes filled with sediment. This usually does not happen, for many reasons:

  1. The sediment is too hard and the core tubes can't break through

  2. The sediment is too rocky and won't stay inside the core tubes

  3. The sediment is nice and muddy at the top, but then changes to a harder sediment, so the core tubes only get filled with a couple inches of sediment

  4. The multicorer itself malfunctions and doesn't work properly at the bottom

Once we get enough good cores- 6 is usually the bare minimum that we like to have, we divide up the cores.

One core goes to looking at oxygen in the sediment- we use a probe that goes into the sediment and measures how much oxygen is there. This is the same probe that we attempted to attach to our ROV and probe the ice with. We don't usually break it when using it in the mud! This core then gets squeezed- pressure gets applied to the top so that the water that is in the sediment gets squeezed out. The water that comes out gets analyzed for nutrients (specifically nitrate and nitrite).

Up to three cores get used for flux cores. These cores are taken into the cold room (a room in the lab on the ship kept at 40 degrees Fahrenheit- like a refrigerator) and set up with tops that have little stirrers on them. Over the course of a few days, the water that sits above the sediment is sampled and analyzed for various nutrients (nitrate, nitrite, ammonia, phosphate and silica) and oxygen. We look at how the concentrations of these things change over the period of a few days- some of them may decrease over time in the water and some of them may increase over time in the water. The decrease tells us that it is getting pulled into the sediment, and the increase tells us that it is getting pushed out of the sediment and into the water column. This is our attempt at simulating the natural environment at the bottom of the Bering Sea, in a much more manageable setting! Heather Whitney is in charge of this part of our experiment, and spends much of her time on the cruise working in the cold room (a room kept at 2 degrees Celsius).

HeatherHeather all bundled up, working in the cold room (2 degrees Celsius) on the flux cores (each long tube you see contains mud and overlying water from a station in the Bering Sea).

After these flux cores are done (usually after a few days), they get frozen in the freezer. We will take them home to Bellingham, WA and use a CT scanner at the local hospital to scan them and look at the animal burrows. The animals are important because they mix up the sediment and cause nutrients to get pulled in and pushed out of the sediment.

The remaining cores get sectioned. This means that we cut them into pieces that are a specific size. We section cores for radon and for nutrients. Radon cores get cut into 2 cm sections- so we start at the top and slice off 2 cm at a time, up to 20cm deep into the core. These slices get put into glass jars that will get hooked up to our "fancy" radon board so we can figure out how much radon is in every 2cm section (because it changes as you go deeper into the core).

Radon BoardThe fancy radon board, where we run our samples for radon. This looks about as complicated as it actually is to run.

Radon JarsRadon jars with sediment, ready to be run on the radon board.

Nutrient cores get sliced every 0.5cm for the first 2cm and then almost every other centimeter after that. Each of these sections gets put into a centrifuge tube. The sediment then goes into a centrifuge that spins the tubes REALLY fast. They spin so fast that the water that is in the sediment (called "pore water") gets separated from the sediment. We take this water and filter it (to make sure it is clean and free from anything solid) and then analyze it for nutrients (again, nitrite, nitrate, ammonia, phosphate, silicate).

Centrifuge TubesCentrifuge tubes, with sediment in them.

I do the filtering in a nitrogen glove bag so that the samples don't get exposed to oxygen. This is important because oxygen can change the chemistry of the nutrients and other things in the sediment and porewater. We want to keep them in the same state as we found them at the bottom of the ocean.

Glove BagThe nitrogen glove bag where I filter my samples. See the centrifuge tubes in there, ready to go.

SamplesRows and rows of filtered nutrients, waiting to be analyzed.

The leftover sediment gets dug out of the tubes and frozen. We will analyze this later on, once we're back at home, for metals such as iron and manganese. These are important because they like to bind to the nutrients in the sediment and keep these nutrients from going into the water column. Nutrients are important in the water column because they provide nutrition for the phytoplankton- which then provides food for the rest of the Bering Sea ecosystem!

Any remaining tubes get sieved for animals- all the mud gets washed away and the animals left behind get preserved so that we can look at them later and determine what species they are.

And that is the day in the life of a mud core- it can take us up to 6 hours to process one station worth of cores, and stations can be as close as 2 hours apart. We just recently sampled two stations in a row, which kept us pretty busy for about 24 hours straight. Luckily we had a couple days off after that, to play catch up!