Polar regions are characterized by a strong seasonality in primary production and thus by a distinct fluctuation in food supply to higher tropical levels. In Arctic marine food webs, the pelagic amphipods Themisto abyssorum and T. libellula represent important links between the herbivore zooplankton community and higher trophic levels; but year-round observations on feeding strategies and lipid storage are lacking. We investigate seasonal variations of lipid classes, fatty acids and gut content of both amphipods collected during summer, fall and winter expeditions to the Fram Strait and Svalbard archipelago (78° to 81°N). Results show a year-round dominance of storage lipids (particularly wax esters and triacylglycerols) over phospholipids for T. abyssorum and T. libellula. High levels of the Calanus markers 20:1 and 22:1 (both isomers) in all seasons indicated that both species are part of the Calanus-based food web. Tracers of diatoms (16:1(n-7) and 20:5(n-3)), ice algae (16:4(n-1)) and dinoflagellates (18:1(n-9), 22:6(n-3)) indicate that the lipid-based energy transfer could be traced back to the respective algal sources. Metabolic demands of the investigated amphipods are sustained by active dietary input (provided in winter mostly by diapausing calanoid copepods such as C. finmarchicus) and the biochemical modification of internal reserves. We highlight that the lipid reservoir of pelagic amphipods and their biochemical modifications seem to buffer seasonal variations in available prey and serve as an effective adaptation to maintain an active, predatory life-style year-round in high Arctic waters.