June 21, 2009
55° 25.977 N
Station 25-CN17 is right on the precipice that is the continental break. Roughly 200 meters in depth, this extremely productive region of the ocean will be one of the more important stations in the cruise. As a result, all of the tests will be run here and the sediment traps deployed.
At 05:00, Pat, Matt, and I poured samples from the rosette for POC at depths of 25, 40, 50, 60, and 100 meters, and at twelve different depths for small volume thorium testing from 1 to 195 meters. Back in the lab, the filtrations were set up and like yesterday, Matt and I went back to retrieve samples from the Prod CTD for Dr. Lomas's project. This time, I was left to tend them on my own from start to finish as Matt and Pat had lots of other things to do. I filtered the 7 solutions in the same fashion as yesterday, and placed them in the freezer for storage.
At 08:30 it was time to launch the sediment traps. The sediment trap is a 100-meter long series acrylic tubes designed to catch anything that drifts down from above. The tubes are set up at depths of 25, 40, 50, 60, and 100 meters and are all tethered together by rope and bungee. Each tube is filled with brine (saturated salt water), which is significantly denser than normal seawater before the traps are placed in the ocean. This ensures that the particles that settle into the tube do not come back out when the traps move with the currents or when they are being pulled back out and onto the ship. The whole assembly is connected to a buoy on top that transmits its position back to the ship every hour. Once the sediment trap has been placed in the water, it is allowed to flow freely for 24 hours before being captured. The trap deployment took the better part of an hour due to the high seas and by the time I write this entry later this evening, it will have drifted almost 15 miles.
Around 11:00 the captain came over the intercom "The weather deck is secure. All personnel must notify the bridge if venturing outside." In other words, don't go outside right now unless you really have to; it's way too risky. The seas are still pretty rough. Last night I could hear things that were not secured falling from shelves in the adjacent rooms. I was careful about the way I slept so as not to get dumped out of my bunk in the middle of the night.
The afternoon saw the completion of the morning filtrations and a second set of CTD casts. We were now in almost 3000 meters of water having passed over the continental slope nearing the start of the abyssal plain. 3000 meters of water is a lot to cover when sampling so the CTD was lowered twice. It took about an hour to lower it to the bottom, almost 10,000 feet below us. One the way back up it made 12 stops completing a round trip that lasted 2.5 hours.
While waiting for the CTD to resurface, a school of Dall's porpoises were spotted off the stern. It looked to be a pack of 10-20 that circled to boat, just barely breaking the surface of the water. Porpoises were not on my original list of things to see. Moose - check. Bald eagles - check. Puffins - check. Whales - no check (but I am still hopeful). I think I will add the porpoises to the list though so I can cross them off.
Small volume samples were taken again, prepped, and filtered. These filtrations went much faster than the previous ones since there is not much particulate matter in the deep ocean. Even if there is a lot of biological activity in the top 200 meters of the water column, the organic carbon that is exported will be used by bacteria, grazed upon by zooplankton, or re-mineralized by the pressure long before it hits the bottom 2 miles below. All of the filtrations finished in less than one hour, four times faster than their shallow water counterparts.
Pat headed to bed and I helped Matt gather the last small volume samples for thorium tests from the shallow CTD cast (200 meters). The porpoises came back for an encore. Back in the lab, Matt asked me to add the reagents this time in case I have to run the whole process later on in the cruise. He had taken a nap earlier in the afternoon in preparation for the night shift and will be staying up for a while to see the filtrations through.
It is now 22:00 and I am starting to get tired. I think I will head to bed soon. The ship will be repositioning after breakfast to capture the traps and I do not have any responsibilities before then. I should be able to sleep in a little and will set my alarm for 06:30.