A survey of carbon monoxide and non-methane hydrocarbons in the Arctic Ocean during summer 2010

[摘要] During the ARK XXV 1 + 2 expedition in the Arctic Oceancarried out in June–July 2010 aboard the R/V Polarstern, we measured carbon monoxide(CO), non-methane hydrocarbons (NMHC) and phytoplankton pigments at the seasurface and down to a depth of 100 m. The CO and NMHC sea-surfaceconcentrations were highly variable; CO, propene and isoprene levels rangedfrom 0.6 to 17.5 nmol L⁻¹, 1 to 322 pmol L⁻¹ and 1 to 541 pmol L⁻¹, respectively. The CO and alkene concentrations as well as theirsea–air fluxes were enhanced in polar waters off of Greenland, which weremore stratified because of ice melting and richer in chromophoric dissolvedorganic matter (CDOM) than typical North Atlantic waters. The spatialdistribution of the surface concentrations of CO was consistent with ourcurrent understanding of CO-induced UV photoproduction in the sea. Thevertical distributions of the CO and alkenes were comparable and followedthe trend of light penetration, with the concentrations displaying arelatively regular exponential decrease down to non-measurable values below50 m. However, no diurnal variations of CO or alkene concentrations wereobserved in the stratified and irradiated surface layers. On severaloccasions, we observed the existence of subsurface CO maxima at the level ofthe deep chlorophyll maximum. This finding suggests the existence of anon-photochemical CO production pathway, most likely of phytoplanktonicorigin. The corresponding production rates normalized to the chlorophyllcontent were in the range of those estimated from laboratory experiments. Ingeneral, the vertical distributions of isoprene followed that of thephytoplankton biomass. These data support the existence of a dominantphotochemical source of CO and light alkenes enhanced in polar waters of theArctic Ocean, with a minor contribution of a biological source of CO. Thebiological source of isoprene is observed in the different water masses butsignificantly increases in the warmer Atlantic waters.

[学科分类] 地球化学与岩石