June 23, 2009
57° 20.94 N
I was down in the main lab by 01:00, coffee in hand. The bongo tow was now scheduled for 03:20 but there was no sense in going back to bed. I used the time to edit my entry for yesterday and organize some photos and before I knew it, it was time to bundle up and head out to the deck.
The bongo net consists of two long, conical nets attached to a single frame. It was lowered into the water from the starboard side to a depth of 30 meters and then immediately brought back to the surface. This angled tow ensures that the nets will pass through the krill layer twice, once on the way down and then again on the way back up. The organisms are funneled through the nets into collection containers (called codends) at the end. Once the nets have been brought back on deck, the contents are poured into an Igloo cooler and the krill and other organisms of interest, including amphipods and fish larvae, are removed. The sorting is done on deck to keep the animals from getting too warm. Krill are hardy organisms as long as they are kept within their preferred temperature range.
Scientists Tracy Shaw and Megan Schatz are collaborating on a project for Dr. Evelyn Lessard of the University of Washington. All of the BEST projects on the Thompson are focused on determining how the Bering Sea ecosystem will change if the ice conditions change. The main goal of Dr. Lessard's project is to understand the specifics of the krill's diet. They are concentrating on whether or not the krill are selectively feeding on specific types or specific species of phytoplankton and microzooplankton. Organisms that live in the sea ice are potentially important as a food source. If the timing of the ice melt changes, this food may be released from the ice when ocean conditions are not right for the ice biota to bloom and become an abundant food source. The organisms then will die off and sink to the bottom becoming part of the benthic cycle.
Tracy and Megan invited me to help separate the krill from the myriad of little critters that were swimming in the cooler. I was given a generic Japanese soup spoon with which to scoop them out and place them in a nearby plastic bowl sitting on ice to keep the water from warming. Five different species of krill are commonly found in this region. Different species can be region specific. Since tonight they were towing in relatively shallow water, it was no surprise that only one was found, Thysanoessa raschii. Catching them and keeping them in the spoon proved to be more difficult than you might think. It was hard not to scoop up other organisms with the krill and once in the spoon, they were very eager to jump right back out. Once the majority of the krill were transferred, they were taken back to the cold room for processing.
The cold room is located just forward (towards the bow of the ship) of the computer room. The size of a small walk-in cooler, it is kept between 4-5°C, the same temperature as the Bering Sea in this region. To study their diet, 2-10 krill (depending on size) are placed in a 2.5-liter bottle of seawater. Samples are collected to measure chlorophyll present (to indicate phytoplankton abundance), and the number and types of phytoplankton and microzooplankton which will be counted under a microscope after the cruise. The 2.5-liter bottles are then brought to the stern of the ship. Secured on the deck here is an incubator tank equipped with flow through seawater. Water is pulled directly from the ocean and circulated through the tanks before being dumped back over the side once again in order to maintain ambient seawater temperature. After slowly rotating for a 24-hour incubation period, the bottles are removed and again brought back to the cold room. Samples are again removed and analyzed for chlorophyll and microzooplankton to determine what the krill fed on. The krill are then frozen and will be sent back to the mainland for further analysis.
At 07:10 the Prod CTD was lowered into the water and I was there to collect. Seven samples of 2 liters each were again taken, brought back to the lab and run through the glass fiber and polycarbonate filters. At 08:00 I was back in the CTD garage to help Pat sample from the standard CTD cast. Because the water is so shallow here on the Bering shelf (only 72 meters) 6 samples were taken for small volume thorium testing. I asked Pat why it is called small volume when we are filtering 4 liters of seawater (4 liters didn't seem that small to me). He told me that the same test years ago used to take barrels full of seawater. Small volume seems logical now. At 14:00 my phytoplankton pigment filtrations finished. I cleaned up and headed to bed to get some sleep. I awoke at 20:00, showered, got dressed, and went to the galley for some breakfast/dinner (depending on your point of view). I looked in the leftover fridge in hopes of finding some of the curried noodles from yesterday's lunch. I was disappointed to find none and instead toasted an English muffin.
Down in the lab the filtrations from the sediment traps were still going, 36 hours strong. The Phaeocystis really did jam up the filters. The bongo tow for this evening is scheduled for 02:20 and there is not much going on. Our next sampling won't occur until the 06:30 Prod CTD cast at station 39-NP1. I am going back to my stateroom to read and try to get another hour or two of sleep.