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Variations in contributions of sinking dead copepods to particulate organic carbon downward fluxes in the Beaufort Sea

Makoto Sampei*, Alexandre Forest, Louis Fortier, Tamiji Yamamoto, Hiroshi Hattori, Hiroshi Sasaki

*Corresponding author:

ABSTRACT: Dead zooplankton, including crustaceans, are increasingly recognized as important agents of vertical carbon export from surface waters and in marine food webs. Quantifying contribution of passively sinking copepods (PSCs) to total particulate organic carbon (POC) vertical flux is important to understanding marine ecosystem carbon budgets. Information on this is limited because identifying PSC in sediment trap samples is difficult. Generally, swimmers (undecomposed metazonans caught in sediment traps including PSCs) are removed from a trap sample before the POC content is measured, although ignoring PSCs causes the total POC flux to be significantly underestimated. We quantified temporal and regional variability in PSC flux and contribution of PSCs to total POC flux (PSCs + detrital sinking particles, generally analyzed to estimate detrital POC flux) at the Mackenzie Shelf margins in the Beaufort Sea. Six datasets were used to examine PSC flux variability at ~100 m depth, which is deeper than the winter pycnocline depth (30–50 m), at the continental margin. The average annual PSC flux (1378 ± 662 mg C m2 y1, n = 6) and PSC contribution to the total POC flux (21% ± 10%, n = 6) suggested that PSCs, especially Pareuchaeta glacialis, were important agents of POC export from the surface layer (~100 m) to deeper water at the inter-regional and multiyear scales. We also proposed hypothesis that processes controlling PSC flux variability may vary seasonally, perhaps relating to life cycle (reproduction) in winter (February) and osmotic stress in July–October when the PSC flux is relatively high.