Jackie Grebmeier has been collecting benthic cores in the Arctic since the mid-1980's and she has continued to make this a part of the Distributed Biological Observatory. Using these core samples, she has been able to create a long-term data set that addresses the diversity and biological characteristics of the benthic ecosystem in the Arctic. On this expedition, Jackie, and her PhD student Christina Goethel, are collecting cores to observe oxygen consumption by the organisms in the mud.
As we go through the DBO lines, the benthic team has been collecting cores at selected sites, particularly where the mud is suitable for collecting relative undisturbed cores and 8 cores are collected each time. In order to obtain a sample, the benthic team uses a core cylinder mounted on a pyramid-shaped metal frame. The metal cylinder has a plastic Plexiglas liner in it that is used to store the core sample. When the corer is lowered into the ocean, heavy 100-lb lead weights on the top of the apparatus help to push the metal cylinder into the mud. Once the corer starts to come up, a metal arm swings down and under the cylinder to keep the mud sample from falling out. All of this has to be timed correctly in order to get enough benthic material on the bottom and some bottom water on the top of the cylinder in each core so that experiments can be performed.
Once on deck, the core is removed in the plastic cylinder and if necessary, trimmed to an optimal size for an incubation experiment. Jackie and Christina are using small fiberoptic oxygen sensors on the plastic cylinders. The mud sample, simulating the sea floor, sits a few inches below this sensor and the sensor measures the dissolved oxygen in the bottom water above the mud cylinder surface. The sensor therefore is positioned to read oxygen levels in the water overlying the mud core.
Jackie and Christina are looking at oxygen consumption using two variables. The cores are being stored in the dark (like on the sea floor) at warm and cold temperatures (two variables) and they are also either being fed or not fed using a commercial shellfish food (two more variables). The control cores are those at sea floor temperatures and without food added so that they can compare to the results of the experimental cores. Their hypothesis is that the organisms in the warmer, fed cores will use oxygen at a higher rate. We will have to follow the data throughout the expedition to find out what their results are.
A Question From the Crow's Nest
Looking at the picture of the mud in the cores above, why is the bottom mud black or much darker than the mud at the surface?
Answer from previous post: Predatory worms have a preboscus that comes out and attacks prey.