Zooplankton respiration and the export of carbon at depth in the Amundsen Gulf (Arctic Ocean)

In arctic seas, lipids accumulated by zooplankton migrants in the surface layer in spring-summer are respired at depth during the winter. The resulting active downward transport of carbon by the 200-1000 and >1000 mu m mesozooplankton fractions was quantified based on 41 biomass and respiration profiles from October 2007 to July 2008 in the Amundsen Gulf (Canadian Arctic Ocean). The small fraction, dominated by CII-CIII Calanus glacialis, represented on average 12% of the overall zooplankton biomass and contributed little to the active transport of carbon by respiration. From April to July, total zooplankton ingested 17-28% of the estimated gross primary production (GPP) in the surface 100 m, and 36-59% of GPP over the entire water column. The large fraction, comprised mainly of CIV, CV and adults Calanus hyperboreus and C. glacialis that accumulate large lipid reserves, was responsible for 89% of grazing. The downward migration of large zooplankton in late summer coincided with a sharp decline in specific respiration rates signaling the start of diapause and the endogenous fuelling of metabolism. From October to April, Calanus migration-respiration actively transported 3.1 g C m(-2) beyond 100 m, a flux that represented 85 to 132% of the gravitational POC fluxes at 100 m from October to July. Our results stress the importance of including active transport by large zooplankton migrants in carbon budgets of the Arctic Ocean.