Hi all- phew, it was a long weekend and I had to recover from it before writing another journal entry. We had a very busy sampling weekend- three coring stations in a row!! You may be asking yourself- why is that a lot? I’d like to give you an in depth look at the life of a mud core here on the Healy so you can see why it takes us so long to process a core, and why three coring stations in a row is A LOT.
At every station there is a plan- we have many instruments that need to be deployed on the ship at every station, and they cannot be deployed simultaneously- meaning that the 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. Sometimes at stations they send out a team onto the ice 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 the multicorer to be deployed. We are lucky enough to have a technician that gets the corer ready for us- this is Chris from Oregon State University (hey, I used to work there!!). He works really hard to make sure that the corer is ready to go over the side and is in proper working order.
Chris on top of the muticorer, hosing it off (photo courtesy of Rob Freyer)
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.
The multicorer with a bad set of cores (see all that murky water and not much mud)
Core 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.
Measuring and selecting cores- yes, that’s me in my orange mustang suit!!
Up to two cores go to looking at oxygen in the sediment- we use a probe that goes into the sediment and measures how much oxygen is there. These cores then get squeezed- pressure gets applied to their tops so that the water that is in the sediment gets squeezed out. The water that comes out gets analyzed for nutrients (specifically nitrate, nitrite and ammonia).
Al and David looking at a squeeze/oxygen profile core (photo courtesy of Jeff Napp)
David profiling a core for oxygen (photo courtesy of Rob Freyer)
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 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.
Bonnie (UW graduate student) setting up the flux cores. She’s all dressed up in her winter gear to brave the chilly temperatures in the cold room!
A set up flux core in the cold room- see the little white stirrer that mixes the overlying water.
After these flux cores are done (usually after a few days), they get frozen in the freezer. We will take them home and use a CT scanner at the 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 the radon board (anyone figure out what we use the cheese grater for yet?) so we can figure out how much radon is in every 2cm section (because it changes as you go deeper into the core).
Robyn and myself slicing a core and putting it into centrifuge tubes.
Radon 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 get 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, etc).
Centrifuge tubes, with sediment in them.
I do most of 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 pore water. We want to keep them in the same state as we found them at the bottom of the ocean.
I’ve showed you this before, but here it is again- the nitrogen glove bag where I filter my samples. See the centrifuge tubes in there, ready to go.
Rows and rows of filtered nutrients, waiting to be analyzed.
Calvin, who runs all our samples for us on the ship. He is a very busy man!!!
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.
Jerry, sieving the mud for animals.
And that is the day in the life of a core- can you see why we are all SO busy when we have to do 3 core stations in a row?!? 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 were very busy this past weekend- most of us tried to catch some zzzzz’s whenever we could! Luckily things are slowing down now…
David, sleeping while running some radon samples.
