The Fecal Pellet fraction of biogeochemical particle fluxes to the deep sea

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Abstract
Fecal pellets produced by suspension‐feeding crustacean zooplankton, specifically copepods and euphausids, have frequently been cited as an important mode of large particle transport in the open ocean. The objectives of the present study were to determine the various biogeochemical fluxes provided by pelagic crustacean fecal pellets, to examine such fluxes as a function of depth and variable levels of surface water productivity, and to assess the overall fecal pellet contribution to oceanic particle fluxes as measured with sediment traps. Pellet subsamples were obtained from particulate samples collected at depths between 389 and 5068 m by moored PARFLUX sediment traps deployed for up to 12 months at three tropical‐subtropical open ocean localities. The sites were located over the East Hawaii Abyssal Plain (P site), over the Demerara Abyssal Plain (E site), and in the Pacific Panama Basin (PB site). Fecal pellet flux and chemical composition were found to vary significantly on a geographic scale as a function of productivity levels in the surface waters. The total carbonate, organic carbon, opaline silica, and lithogenic fluxes provided by pellets at the oligotrophic P1site were 1–2 orders of magnitude less than that measured at the eutrophic station in Panama Basin. The pellet data show that contrary to previous assumptions, these biogenic aggregates are responsible for no more than 5% of the total mass flux of oceanic particulate material. Despite the fact that at all trap depths, large numbers of intact pellets were collected which displayed minimal effects of dissolution and microbial degradation, fecal pellets contributed an average of only 1–10%, 0.5–5%, 1–3%, and 0.5–4% to the total measured mass fluxes of organic, carbonate, opaline silica, and lithogenic material, respectively. However, the pellets showed elevated C/N ratios (9–14) as well as high organic content (representing up to 50% of the individual pellet weight), suggesting that they constitute an important source of organic carbon for the deep‐sea benthos. Rapid remineralization of the organic‐rich pellets must occur at the deep‐sea sediment/water interface, as these biogenic aggregates were completely absent from all site core tops.