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F.lux vs twilight7/25/2023 Zooplankton play diverse roles in the cycling of many elements in the ocean including iron, zinc, sulfur, and mercury ( Fowler, 1977 Asher et al., 2016 Baines et al., 2016 Schmidt et al., 2016 Gorokhova et al., 2018). Our results highlight the need for a greater research focus on the many taxa that potentially act as flux feeders in the oceanic twilight zone. This implies a substantial impact on slowly sinking particles, but a negligible impact on the presumably rapidly sinking fecal pellets that comprised the majority of the material collected in sediment traps. In contrast, suspension-feeding zooplankton in the mesopelagic (including copepods, euphausiids, appendicularians, and ostracods) had combined clearance rates of 2–81 L m -3 day -1 (mean of 19.6 L m -3 day -1). helicina, meanwhile, could intercept 0.45–1.6% of carbon flux/10 m, which was slightly greater (on average) than the Aulosphaeridae. The maximum flux attenuation attributable to Aulosphaeridae reached 4.2%/10 m when these protists were most abundant. The mean flux attenuation attributable to Aulosphaeridae was 0.69%/10 m (median = 0.21%/10 m, interquartile range = 0.04–0.81%) at their depth of maximum abundance (∼100 m), which would equate to ∼10% of total flux attenuation in this depth range. The two flux-feeding taxa considered in this study could account for a substantial proportion of this flux near the base of the euphotic zone. This equated to approximately 6–10% of carbon flux remineralized/10 m. We found that CFA in the shallow twilight zone typically ranged from 500 to 1000 μmol organic C flux remineralized per 10-m vertical depth bin. These estimates were compared to direct measurements of carbon flux attenuation (CFA) made using drifting sediment traps and 238U– 234Th disequilibrium. Using allometric–scaling relationships, we computed the percentage of carbon flux intercepted by flux feeders and suspension feeders. To quantify the potential impact of two flux-feeding zooplankton taxa and the total suspension-feeding zooplankton community, we measured depth-stratified abundances of these organisms during six cruises in the California Current Ecosystem. In contrast to typical suspension-feeding zooplankton, flux-feeding taxa preferentially consume rapidly sinking particles that would otherwise penetrate into the deep ocean. However, the impact of different taxa depends on their feeding mode. Zooplankton are important consumers of sinking particles in the ocean’s twilight zone. 4Laboratoire d’Océanologie et de Géosciences, Wimereux, France. ![]() 3Scripps Institution of Oceanography, University of California, San Diego, San Diego, CA, United States.2Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, FL, United States.1Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, FL, United States.
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