Wednesday, February 18, 2015

Food for the Deep Sea – Recovery of our Sediment Trap Mooring After Sixteen Months in the Deep Dark Sea

Recovered sediment trap with sinking detritus
in the sample bottles from the past year.

Nearly all of the deep-sea floor is fed by a rain of dead organisms, plankton, fish, and whales sinking from the productive surface waters of the ocean.  Sediment traps are used to measure this rain of food, catching sinking particles in large inverted plastic cones. We deployed  two sediment traps at a mooring in an abyssal study area in October 2013, and returned two days ago to recall it from the ocean bottom more than 2 miles (>4000 m) down.  Recovery of such mooring is always nerve racking – many things can go wrong over the course of 16 months due to corrosion, battery failures, or fouling of our moorings on debris at the seafloor.

Craig Smith (left), Clifton Nunnally (right), and 
Andrew Sweetman (back) working on
sediment trap during recovery.
To our delight, our sediment trap mooring responded immediately to our acoustic commands, rising rapidly to the ocean’s surface within 1.5 hours.  The recovery was smooth and we were presented with 42 sample bottles that had captured the sinking flux of food to the deep-sea over the course of one year (see image above). The “food” was brown flocculent material covering the bottom of our 1-liter sample jars, resembling the dust that accumulates in the dirty corner of your basement. Ahh, but this is delightful sustenance for the starved animals living in the cold, dark deep sea! These samples will tell us the quantity and quality of food material reaching the sea cucumbers and brittle stars of the inky depths, helping us to understand how they might respond to changes in their food availability resulting from sediment plumes from deep-sea mining.

Written by: Craig Smith (Chief Scientist) - University of Hawaii at Manoa

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