In spite of its harsh climate, the Antarctic Seasonal Sea Ice Zone (SIZ) is remarkably diverse and hosts globally significant fisheries resources, such as Antarctic krill (Euphausia superba). Large populations of penguins, other birds, seals and whales symbolize the biological richness of this ecosystem. Today, the distribution of sea ice is beginning to alter in some Antarctic regions due to global warming. It is therefore imperative to understand the ecological significance of sea ice in order to better predict future changes of Antarctic marine ecosystems. The production of ice algae is probably fundamental to sustain the rich life of the Antarctic Sea Ice Zone. Thus, the biological resources from the ice must be transferred into the pelagic food web by species feeding at the ice-water interface. Investigations with a newly developed Surface and Under Ice Trawl (SUIT) yielded the first large-scale multi-seasonal evidence that life at the ice-water interface is surprisingly diverse and abundant. Especially Antarctic krill was closely associated with the underside of sea ice. Comparison with deeper fishing nets showed that the ice-water interface hosts its own species community, hitherto unavailable for quantitative sampling. The composition of this community strongly responds to sea ice properties. These results indicate that both macro- and mesozooplankton play a significant role as trophic energy transmitters between the sea ice and the mesopelagic food web. These findings provide new and direct evidence that sea ice is an important structuring force in the Southern Ocean ecosystem and allow new insights in the response of Antarctic marine ecosystems to changing sea ice characteristics caused by global warming. Consequences for the conceptual view of the pelagic food web in the SIZ are highlighted and future research perspectives are discussed.