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 μ 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.