Intense photooxidative degradation of planktonic and bacterial lipids in sinking particles collected with sediment traps across the Canadian Beaufort Shelf (Arctic Ocean)
1Aix-Marseille Univ., Mediterranean Institute of Oceanography (MIO), UMR7294, CNRS/INSU, UMR235, IRD, 13288, Marseille, Cedex 09; Université du Sud Toulon-Var (MIO), 83957, La Garde cedex, France
2Université Laval, Takuvik CNRS-Laval U. Joint Laboratory, 1045 av. de la Médecine, Québec, Quebec G1V 0A6, Canada
3Centre de Formation et de Recherche sur l'Environnement Méditerranéen (CEFREM, UMR5110 CNRS), Bât. U, Université de Perpignan, Via Domitia (UPVD), 66860 Perpignan, France
Abstract. The lipid content of seven samples of sinking particles collected with sediment traps moored at ~100 m depth in summer and fall across the Canadian Beaufort Shelf (Arctic Ocean) was investigated. Our main goal was to quantify and characterize the biotic and abiotic degradation processes that acted on sinking material during these periods. Diatoms, which dominated the phytoplanktonic assemblage in every trap sample, appeared to be remarkably sensitive to Type II (i.e. involving singlet oxygen) photodegradation processes in summer, but seemed to be relatively unaffected by biotic degradation at the same time. Hence, the relative recalcitrance of phytodetritus towards biodegradation processes during the Arctic midnight sun period was attributed to the strong photodegradation state of heterotrophic bacteria, which likely resulted from the efficient transfer of singlet oxygen from photodegraded phytoplanktonic cells to attached bacteria. In addition, the detection in trap samples of photoproducts specific to wax ester components found in herbivorous copepods demonstrated that zooplanktonic faecal material exported out of the euphotic zone in summer were as well affected by Type II photodegradation processes. By contrast, sinking particles collected during the autumn were not influenced by any light-driven stress. Further chemical analyses showed that photodegraded sinking particles contained an important amount of intact hydroperoxides, which could then induce a strong oxidative stress in underlying sediments.