11/30

November 30, 1999

Megacore being launched off the stern.

Our 72 hour tour on station at FB#3 is coming to a close, and we are about to head southeast to the second station for another 3-day rotation. The goal is to repeat the sampling procedures at three sites during the length of the cruise and , indeed, on each of the 4 subsequent cruises, through February, 2001. In this way, DeMaster and Smith hope gain a clearer understanding of the bloom production pulse and the broader impact on seafloor communities and nutrient cycling as part of the bigger picture of Antarctic ecology.

Meanwhile, the days have already begun to merge into a cycle of core launches and retrievals, punctuated by meals and fitful periods of brief sleep. The ship's soundscape is a continuous racket of engines, winches, sonar and the hum of the ventilation system. Added to this are the frequent, short bursts of the ship's bow thrusters, which are employed to keep the ship "on station" and in a stable position while cores are deployed and brought up.

Detail of the megacore. When the core penetrates the sediment and is pulled out, the brown catch drops to the bottom, sliding across the opening while the trap door at the top seals the sample.

While everyone is looking sleep deprived, the camaraderie amongst the watches is coming together. The pitcrew efficiency of getting the cores ready and processed is a choreographed interaction: we seem to get better with practice...

The sheer weight and unruliness of the box core, combined with a fairly low success rate makes working on the mega core seem like a vacation. The mega core is a spidery contraption comprising a metal armature and a set of individual cylindrical PVC coring tubes (see above). Each sampling tube comes with its own capture and sealing assembly which is triggered when the rig is pulled from the sediment bed (see right). The device resembles a precision engineered Rube Goldberg affair destined for Mars. Generally, eight to twelve sampling tubes are prepared per cast.

With each megacore launch, between 5 and 12 sample tubes are divided between various members of the teams. The exact number depends on how successful each cast is. Some tubes do not open properly, or do not seal, or are not a contiguous, intact sample. Hopeully, with enough attempts, there will be more than enough sediment to meet everyone's needs. Simth's group will be focusing mostly on the biological aspects of the research and DeMaster's group will be looking at the geochemical dimension of sedimentation and nutrient cycling.

Nicola Mitchell (left) from the British Museum of Natural History and Sarah Mincks (right) from the University of Hawaii, prepare 1cm slices of sediment from a megacore.

With 4 or 5 megacores attempted at each of the three sites, the hope is to measure a number of parameters related to the problem. These include obtaining vertical profiles of 234Th (a Thorium tracer with a relatively short half life), 210Pb (a lead tracer with a much longer half life). By looking at these different tracer elements, and their different rates of decay, researchers will be able to arrive at some understanding of how nutrient cycling works over time as well as in the ways in which processes unfold within layers of the seabed. They will also measure chlorophyll a, amino acids (which are described in terms of bioavailability), microbial mass (measured in terms of the amount of adenosine triphosphate, or ATP), dissolved inorganic carbon (DIC), and biogenic silica. The megacores will be examined for seabed regeneration and oxygen consumption rates, by incubating the core samples for several days. Scientists will also look at how oxygen is distributed in the seabed, as well as several other key factors including ascertaining how porous the sediment is at various depths.