Downward transport of organic carbon by diel migratory micronekton in the western equatorial Pacific: its quantitative and qualitative importance

Using simultaneous sampling with a commercial-sized trawl, a zooplankton net, and a sediment trap, we evaluated the contribution of vertically migrating micronekton to vertical material transport (biological pump) at two stations (3 degrees 00'N, 146 degrees 00'E and 3 degrees 30'N, 145 degrees 20'E) in the western equatorial North Pacific. The gravitational sinking particulate organic carbon flux out of the euphotic zone was 54.8 mg C m(-2) day(-1), The downward active carbon flux by diel migrant mesozooplankton was 23.53 and 9.97 mg C m(-2) day(-1), and by micronekton 4.40 and 2.26mg C m(-2) day(-1) at the two stations. Assuming that the micronekton sampling efficiency of the trawl was 14%, we corrected the downward carbon flux due to micronekton respiration to 29.9 and 15.2mg C m(-2) day(-1), or 54.6 and 27.7% of the sinking particle flux at the two stations. The corrected micronekton gut fluxes were 1.53 and 0.97mg C m(-2) day(-1). The role of myctophid fish fecal matter as a possible food resource for deep-sea organisms, based on its fatty acid and amino acid analysis, is discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.