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Typically, all undecomposed metazoans found in formalin-poisoned cups of sediment traps are considered to be active intruders (or 'swimmers') and are removed to prevent an overestimation of the downward particle flux. However, intact metazoans dead before entering the trap should be included in the estimation of downward flux of carbon. Arctic copepods collected in the field were killed either by formalin to mimic death by actively swimming into the formalin-poisoned cups, or by crowding or high temperature and then preserved in formalin to simulate death before entering the trap. In the crowding and heat treatments, 64% of Calanus hyperboreus and C. glacialis and 44% of Pareuchaeta glacialis differed from copepods killed by formalin in the postmortem posture of the antennules or swimming legs. These frequencies were used to estimate the contribution of passively sinking copepods (PSCs) to the particulate organic carbon (POC) flux measured by a sediment trap moored at 70 m in the Beaufort Sea (Canadian sector of the Arctic Ocean). PSCs represented only a small fraction (<5%) of the copepods collected in the trap, thus justifying the removal of swimmers from samples to avoid a massive overestimation of fluxes. Nevertheless, PSCs contributed 36% of the overall POC flux of 6.8 g C m-2 yr-1, and discarding them along with the swimmers would have resulted in a significant underestimation of downward export. Given their rich carbon content (up to 50%), PSCs could be an important food resource for pelagic and benthic scavengers. [ABSTRACT FROM AUTHOR]

A variable fraction of fecal pellets produced in the epipelagic layer is intercepted and retained before reaching the bottom. We assessed fecal pellet retention in the ice-covered Beaufort Sea in early February by comparing the shape and size-frequency distribution of pellets collected by a sediment trap moored at 210 m to that produced in vitro. Appendicularian ellipsoidal and copepod cylindrical pellets made up 75 and 24% of the flux (165 μg C m−2 day−1). In contrast, production (135 μg C m−2 day−1) was dominated by cylindrical pellets (93%). The vertical flux of cylindrical pellets at 210 m was attenuated by 70%. Pellets >120 μm in width, represented 42% of the production, but were not detected in the trap. Retention most likely resulted from coprorhexic feeding by copepods such as Metridia longa. Our observations suggest that the detritivore food web prevailing under the ice of the Arctic Ocean in winter is dominated by appendicularians feeding on pellets fragmented by copepods. [ABSTRACT FROM AUTHOR]

In the Arctic Ocean, vertical fluxes of particulate organic carbon (POC) remain low during the dark winter period because POC fluxes are derived from photosynthetic production. Passively sinking dead copepods are traditionally excluded from POC fluxes estimated using sediment traps, resulting in the underestimation of the total POC flux. Here, we present the seasonal variability of total POC export flux measured by a sediment trap moored at ~ 100 m in the Amundsen Gulf (southeastern Beaufort Sea) over October 2007-July 2008. Surprisingly, the integrated total POC flux for February (466 mg m-2) was the second highest flux during the study period (the highest was in Jul; 1015 mg C m-2) due to a contribution of 91% from sinking dead copepods. The total POC flux in February 2008 in the Amundsen Gulf was up to two orders of magnitude higher than the previously reported traditional POC winter fluxes that did not include the contribution of sinking dead copepods. Hence, the POC flux in February only could be equivalent to ~ 18% of the quasi-annual traditional POC flux. Our observations suggest that a substantial POC export flux occurred during winter 2007-2008 due to zooplankton life cycle. [ABSTRACT FROM AUTHOR]