Tuesday Afternoon: A Better Mouse Trap

Capturing Sinking Particles In The Twilight Zone

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A neutraly bouyant sediment trap
A neutrally bouyant sediment trap is recovered from a dive. (K. Buesseler, WHOI)




 

If you’re material floating around on top of the water column and decide it’s time for a vacation down deep, there are only two ways to get there. Become entrapped in a descending current, or hitch a ride on another particle already making the trip. In yesterday's entry about the EDDIES program I mentioned that diatoms have the capacity to take in carbon dioxide from the atmosphere and sequester it in the ocean. The VERTIGO  program seeks to help quantify the vertical transport of particles such as these so that the fluxes from shallow to deep water of certain compounds like CO2 can be accurately measured.

In today’s session, titled Sinking Particle Fluxes In The Twilight Zone, presenters discussed various facets of sinking particles, from how fast they descend and how far down they travel to who is eating what along they way. One of the key members of VERTIGO, WHOI’s Ken Buesseler, presented a synopsis of what the program has produced to date. Ken showed how the use of neutrally buoyant sediment traps (NBST) have allowed for a much more accurate way to capture “marine snow.”

Manufactured at WHOI under the engineering direction of Jim Valdes  and using instrument technology developed for the profiling SOLO floats, the resulting device was described by Ken as “an engineering triumph.” Where older sediment traps moored to the bottom would be pulled over by currents and subject to vertical pumping due to wave action, the new instruments drift with the water column at a predetermined depth to give a more accurate picture of what is falling down upon it.

Tools like this give Pheobe Lam, a recent addition to the WHOI scientific staff, the ability to infer what is happening in the water column by looking at the size and composition of fecal material raining down from above. Her findings show that in one location there were high concentrations of large fecal pellets at a depth of 136 meters (450 feet), but by 180 meters (594 feet) they were mostly gone. Now, I normally wouldn’t care what species of marine creature finds fecal pellets an appetizing meal (based on my experience with domestic animals I would put my money on the dogfish) but from what I learned listening to the VERTIGO crowd, I think it’s worth finding out.



 

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Last updated February 24, 2006
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