Defecation by Salpa thompsoni and its contribution to vertical flux in the Southern Ocean
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Measurements of the defecation rate of Salpa thompsoni were made at several stations during two cruises west of the Antarctic Peninsula in 2004 and 2006. Rates were quantified in terms of number of pellets, pigment, carbon and nitrogen for a wide size range of both aggregate and solitary salps. Measured defecation rates were constant over several hours when salps were held at near-surface conditions from which they had been collected. The defecation rate per salp increased with both salp size and the ambient level of particulate organic matter (POM) in the upper water column. The weight-specific defecation rate ranged between 0.5 and 6% day−1 of salp body carbon, depending on the concentration of available particulate matter in the water. Carbon defecation rates were applied to biomass estimates of S. thompsoni to calculate daily carbon defecation rates for the populations sampled during the two cruises. Dense salp populations of over 400 mg C m−2 were calculated to produce about 20 mg C m−2 day−1, comparable to other major sources of vertical flux of organic material in the Southern Ocean. Measured sinking rates for salp fecal pellets indicated that the majority of this organic material could reach deep sediments within a few days, providing a fast and direct pathway for carbon to the deep ocean.
KeywordsSouthern Ocean Particulate Organic Matter Fecal Pellet Vertical Flux Defecation Rate
We wish to thank the many people who worked in support of this project as divers, laboratory assistants and technicians. Included in this group are Erich Horgan, Jeff Godfrey, Jeff Mercer, Kerri Scolardi, Wally Fulweiler, Kelly Rakow and Sandy and Izzie Williams. We are grateful to the crew of the ASRV Laurence M. Gould for their support and the comments of three anonymous reviewers. This study was funded by NSF grants OPP-0338290 to P. Kremer and OPP-0338090 to L. Madin.
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