"A Note on the Science of Sediment Traps"

David Karl

(A note for teachers and older students from oceanographer David Karl on the Science of Sediment traps -- see Deane's Journal from the Polar Duke, for the hair-raising tale of recovering the traps and the winch mishap!)

Sediment Traps

Along with the automatic weather station data, they are THE ONLY YEAR LONG activity in our Long-Term Ecological Research project. Antarctica is well known for its change of seasons even though the leaves do not fall. Scientific information collected during austral winter is sparse and the LTER personnel are not in the field at this time. However, the weather stations and the sediment trap moorings continue their duty.

In the case of the sediment traps, we have a built in computer that directs the operation from under the sea. At a series of predetermined times that I program into the seabed computer, the trap computer sends a pulse to the trap rotary motor and a new sample cup is moved into position. This continues until all 21 separate samples are collected and successfully back on board ship for further analyses. Once the computer is reprogrammed and new sample bottles are positioned on the rotation plate, the entire array is redeployed for another year of data collection.

The sediment traps are essentially worthless on the deck of the ship -- hence our desire and efforts to "turn them around" as quickly as possible. The samples are transported to our home laboratories for a systematic and comprehensive analysis of bioelements (life's building blocks) -- carbon, nitrogen, phosphorus, silica, as well as other lithogenic phases. We view the sample materials under the microscope for characterization of the organic and inorganic matter that is collected.

Why do we care about this? The ability of the ocean to sequester atmospheric carbon dioxide -- rising in response to humanity's use of the planet's fossil fuel stores -- is largely dependent upon the rate of export of organic matter from the near surface waters of the sea. This process, called the biological pump, ultimately fuels all (or in effect most, excluding the deep sea hydrothermal vents) subeuphotic zone (below the lighted zone) organisms and is a vital measurement in fisheries' oceanography. As mentioned above, this is also the mechanism whereby carbon is sequestered into the deeper portions of the world ocean and represents the primary oceanic sink (although perhaps only temporary - 100-1000 years) for fossil fuel.

This is an important area of contemporary oceanography and our efforts in Antarctica are part of an international network of particle flux experiments currently underway. The sediment trap research is part of the "microbiology and carbon flux" component of LTER. In addition to this work, we also measure all pools of carbon in the sea (the largest are dissolved inorganic and dissolved organic carbon) and we make inventories of the numbers and metabolic activities of microorganisms from bacteria to protozoans, including viruses. These data collectively define the microbial loop or microbial foodweb that is so vital to the economy of the sea both in Antarctica and elsewhere.

We also conduct a similar set of experiments at a subtropical North Pacific Ocean site, called Station ALOHA (A Longterm Oligotrophic Habitat Assessment). This research is also funded by NSF and is a North Pacific barometer for global environmental change. We visit that site about once per month and have been doing so since Oct 1988. The Hawaii effort is called "Hawaii Ocean Time-series" (HOT), and the Antarctica effort is called "Coupled Ocean-ice Linkages and Dynamics" (COLD); hence the lab logo, HOT & COLD! You can learn more at my homepage:


Hope this helps.

David Karl
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