Richardson, Tammi L.¹, George A. Jackson², Hugh W. Ducklow³ and Michael R. Roman⁴

¹Department of Oceanography, Texas A&M University, MS 3146, College Station, TX, 77843-3146, Tel: 979-845-2977, Fax: 979-845-8219, E-mail: tammi@ocean.tamu.edu, ²Department of Oceanography, Texas A&M University, MS 3146, College Station, TX, 77843-3146, ³Virginia Institute of Marine Science, P.O. Box 1346, Gloucester Point, VA 23062 and ⁴Horn Point Environmental Laboratory, University of Maryland, P.O. Box 775, Cambridge, MD 21613

Planktonic food webs of the eastern equatorial Pacific: a synthesis of EqPac time-series carbon flux data

We used an inverse analysis approach to examine carbon flow through planktonic food webs of the eastern equatorial Pacific. This approach allowed us to synthesize data from the EqPac Time-Series cruises into a complete picture of picture of carbon cycling, and to examine the role of different food web components in controlling trophic transfers, particle export, and DOC production in this region. The modeled webs included four phytoplankton groups (picoplankton, diatoms, pelagophytes and prymnesiophytes), three zooplankton groups (protozoa, microzooplankton and mesozooplankton), bacteria, DOC, detritus, and a compartment for carbon export out of the euphotic zone. Calculations using data from TS1 (March-April 1992) showed that protozoan grazers (< 20 μm in size) directly consumed 43% of the total primary productivity. Picoplankton made up > 60% of the protozoan diet (the remainder being bacteria, detritus, and pelagophytes). In these models we assumed that the mesozooplankton (> 200 μm grazers; primarily copepods) did not graze the picoplankton directly. However, calculations showed that the mesozooplankton played an important indirect role in the export of picoplankton carbon through their consumption of protozoa and microzooplankton: approximately 10 mmol C m^-2 d^-1 of the 83 mmol C m^-2 d^-1 of picoplankton primary production was exported indirectly through mesozooplankton path. The inverse analysis approach allowed us to estimate flows within the system that were not measured directly. DOC advection out of the system, for example, was calculated to be ~ 17 mmol C m^-2 d^-1 which is roughly twice previous estimates.