Intense photooxidative degradation of planktonic and bacterial lipids in sinking particles collected with sediment traps across the Canadian Beaufort Shelf (Arctic Ocean)

摘要

The lipid content of seven samples of sinking particlescollected with sediment traps moored at ~ 100 m depth insummer and fall across the Canadian Beaufort Shelf (Arctic Ocean) wasinvestigated. Our main goal was to quantify and characterize the biotic andabiotic degradation processes that acted on sinking material during theseperiods. Diatoms, which dominated the phytoplanktonic assemblage in everytrap sample, appeared to be remarkably sensitive to Type II (i.e. involvingsinglet oxygen) photodegradation processes in summer, but seemed to berelatively unaffected by biotic degradation at the same time. Hence, therelative recalcitrance of phytodetritus towards biodegradation processesduring the Arctic midnight sun period was attributed to the strongphotodegradation state of heterotrophic bacteria, which likely resulted fromthe efficient transfer of singlet oxygen from photodegraded phytoplanktoniccells to attached bacteria. In addition, the detection in trap samples ofphotoproducts specific to wax ester components found in herbivorous copepodsdemonstrated that zooplanktonic faecal material exported out of the euphoticzone in summer were affected by Type II photodegradation processes as well.By contrast, sinking particles collected during the autumn were notinfluenced by any light-driven stress. Further chemical analyses showed thatphotodegraded sinking particles contained an important amount of intacthydroperoxides, which could then induce a strong oxidative stress inunderlying sediments.