November 29, 1999

As I described earlier (see November 21), DeMaster and Smith and their respective teams are interested in trying to evaluate the fate of seasonal bloom particulate matter: how it accumulates and how it has an impact on benthic, or seafloor, communities. Their project is undertaken with a view to testing four hypotheses:

1. That nearly half of the organic material produced during the spring/summer bloom period is deposited on the west Antarctic Peninsula shelf as phytodetritus or fecal matter, usually pellets.

2. That the deposited bloom material serves as a viable source of particulate organic carbon (POC), or quite literally a "foodbank," which is used during the famine months ahead.

3. That large amounts of POC are churned over in the sediment by the feeding and food caching activities of seafloor creatures.

4. That macrobenthic detritivores, or tiny bottom feeders, undergo a dramatic jump in overall abundance following the bloom and associated pulse of POC.

Group inspects the contents of a box core.

With the efforts of the first watches underway, we all were faced with learning new skills and how to effectively work together in teams. My contributions would be in helping out on deck with launching and retrieving the various coring devices that would be used to gather samples for analysis. Given the nature of the research, considerable attention would to be paid to getting the sediments, intact, from the seafloor on to the ship--often while the ship was being tossed in rough seas. Simply scooping up buckets full of mud would not not be helpful.

One of the devices with which we would become intimately familiar is a box core, "Penelope" as she was fondly christened by Beth McAndrews. The box is itself stainless steel, measuring 50cmX50cmX60cm. The bottom and top are open, with two parallel sides of the bottom fashioned with a shallow, convex curve. The bottom edges are also slightly bevelled, so that they can cut into the sediment. The box, in turn, is mounted into what may be described as a passive pile driver (which uses gravity and its weight rather than any mechanical advantage). These elements are mounted on a sled. When the rig is lowered into the depths and settles on the floor, the box and pile driver are released. A large rubber padded steel shovel is designed in such a way so as to be cocked in an open position during decent and then to pivot down and seal the bottom of the box when the rig is pulled up from the seafloor. There are two steel doors above the open box remain open during lowering are connected by bungey cords. When the box penetrates the sediment, they are released into a closed position, effectively sealing the sample. While the seal is not water tight, it is designed to prevent disturbance to the sediment surface.

Craig Smith (left) and Paulo Sumida (right) work on the release mechanism of the box core.

The goal in a succesful box core operation is to get a relatively undisturbed section of the seafloor, with the interface to the water column intact. This is not easy in a ship that is being tossed in 10-20 waves. If the box core plunges too deeply into the sediment, the interface is lost; if it bounces off the floor, or gets jerked around on the ascent, the interface gets transposed or all mixed up and the sample is no good. It is truly a series of finesse moves, with a very heavy and unwieldy item.

Once a box core is retrieved, a group of 3-5 of us go to work like a pit crew: securing the coring device on the deck, draining excess water off sample and delivering it to waiting researchers who will sift through the mud. In this, different groups get samples to examine different aspects of the sediment, from macrofauna inventories and biomass/abundance scans to carbon flux measurements.