Project SANTA CLAµS
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Accomplishments & Reports: The Palmer-LTER Sediment Trap ExperimentD. M. Karl and T. Houlihan University of Hawaii, SOEST, Department of Oceanography Honolulu, HI 96822 (dkarl@soest.hawaii.edu) The continuous production of biogenic matter in the near surface waters of the world ocean ultimately sustains the downward flux of particles at all ocean depths. Particle flux measurements conducted in a variety of coastal, oceanic and ice edge habitats of the Southern Ocean have revealed tremendous seasonality and large interannual variability. For example, spring bloom exports of particulate carbon in coastal Antarctica may exceed 30 mmol C m-2 d-1 (Karl et al. 1991) compared to late winter fluxes of < 1 x 10-4 mmol C m-2 d-1 (Fischer et al. 1988). Furthermore, the variance in the magnitude of the spring-summer export peak can change by an order of magnitude over consecutive years (Wefer 1989). It is not known whether interannual variability is driven by changes in particle formation (i.e., primary production) or by uncoupling of production and exportation, or both. These production-export processes can exert a major influence on global carbon and associated cycles of bioelements. Consequently, the processes controlling particle production, particle export and in situ mineralization in Southern Ocean habitats are topics of great interest in contemporary oceanography. As one component of the Palmer Long-Term Ecological Research (LTER) program, we established three sediment trap sites: two within the central portion of Palmer Basin near Victor Hugo Island (64° 29.49'S, 65° 59.14'W and 64° 28.66'S, 65° 57.44'W) and the third in Crystal Sound (66° 10.045'S, 66° 25.165'W). Each mooring array is constructed of 220 m of DacronR braid (0.5" diameter) with a single McLane Research Laboratories 21-cup sequencing sediment trap (PARFLUX model #MK-7) positioned 176 m above the seafloor and a single Benthos acoustic release (model #865) positioned 20 m above the seafloor. Buoyancy was controlled by 7 glass floats (17" diameter) and a 250 kg expendable concrete anchor. Moorings were set during the LTER annual cruise in Jan 1994 and were recovered, successfully, during SANTA CLAµS. For reasons that were not immediately obvious in the field, one of the replicate traps deployed in Palmer Basin failed to operate. During Project SANTA CLAµS, we also successfully redeployed a single mooring, containing two traps and equipped with a dual acoustic release mechanism, in Palmer Basin (64° 29.846'S, 66° 02.541'W) and deployed and recovered a short-term mooring (17-22 Dec 1994) in Paradise Harbor (64° 50.533'S, 62° 53.823'W). The short term experiment was successful and showed large differences in flux over relatively short intervals of time (6-12 hrs). Whether this is the result of diel krill (and other zooplankton) grazing processes will be investigated once the samples are returned to our home institution. After receipt of sample materials, the formalin-preserved collections will be analyzed for total mass, particulate carbon, nitrogen, phosphorus and silica, and dissolved nutrients. Subsamples will also be analyzed for bacteria, phytoplankton and viruses. ReferencesFischer, G., D. Fuetterer, R. Gersonde, S. Honjo, D. R. Ostermann and G. Wefer. 1988. Seasonal variability of particle flux in the Weddell Sea and its relation to ice cover. Nature, 335: 426-428. Karl, D. M., B. D. Tilbrook and G. Tien. 1991. Seasonal coupling of organic matter production and particle flux in the western Bransfield Strait, Antarctica. Deep-Sea Research, 38: 1097-1126. Wefer, G. 1989. Particle flux in the ocean: effects of episodic production. In: W. H. Berger, V. S. Smetacek and G. Wefer (eds.), Productivity of the Ocean: Present and Past, John Wiley & Sons, New York, pp. 139-153. |