Contribution of zooplankton faecal pellets to carbon transport of the mesopelagic layers in the polynya region of Prydz Bay, Antarctica

摘要

Seasonal changes in the zooplankton swimmer (those actively swimming into sediment traps) and faecal pellet contribution to particulate organic carbon (POC) were analysed based on sediment trap samples deployed at 450 m in the polynya region of Prydz Bay during March 2013-February 2014. The zooplankton swimmer flux ranged from 6.18 ind m(-2) day(-1) to 20.00 ind m(-2) day(-1) and pteropods (mainly Limacina helicina) were the most abundant group. Part of the L. helicina population could make a large contribution to the organic carbon flux by passive sinking after death during the austral autumn and winter. The potential contribution of sinking L. helicina to the POC flux could reach 15.21% during winter. Four types of faecal pellets were found: cylindrical, round, ellipsoidal and ovoid. The faecal pellet carbon flux (0.01-4.36 mg C m(-2) day(-1)) contributed 5.54%-62.00% of the POC flux. Cylindrical faecal pellets, which had low abundance in winter but higher abundance in the early austral summer, were attributed to the ice krill Euphausia crystallorophias. The faecal pellet carbon flux showed a high value (1.03 mg C m(-2) day(-1)) but made little contribution (9.18%) to the POC flux during early summer (December) in relation to the large amount of ungrazed algae. The high faecal pellet carbon flux (1.98 mg C m(-2) day(-1)) during mid-summer (January) made the greatest contribution (62.00%) to the POC flux. During autumn and winter, the faecal pellet carbon flux was low and ovoid pellets (mostly generated by L. helicina) were the most abundant. The occurrence of intact fresh pellets and faecal fluff (degraded faecal pellets) in the winter samples suggested that zooplankton activities (diel vertical migration and fragmentation of faecal pellets) had an effect on the carbon flux. The results demonstrated that zooplankton could play an important role in the carbon flux in the polynya region of Prydz Bay.