At high latitudes, thecosome pteropods (marine pelagic mollusks) can dominate zooplankton communities and are important food web components. Due to their calcium carbonate shell made of aragonite, they significantly contribute to ocean carbon flux and are particularly vulnerable to ocean acidification. Despite their prominent role in the pelagic ecosystem, knowledge on the importance of thecosome pteropods for the Weddell Sea zooplankton community is scarce. Furthermore, aragonite undersaturation (Ωar < 1) events are projected to rapidly increase in frequency and duration in the Antarctic Weddell Sea by 2050 due to uptake of increasing amounts of anthropogenic CO2. This potentially perils thecosomes by inducing shell dissolution. The project aim was to describe the importance of thecosome pteropods in terms of their biomass contribution relative to that of the other higher taxonomic mesozooplankton groups in the Weddell Sea pelagic ecosystem and to describe the current shell dissolution state of thecosome pteropods in relation to prevailing ocean carbonate chemistry conditions as a benchmark for possible future monitoring of ongoing ocean change processes. This dataset includes biomass (dry mass, nitrogen and carbon mass) of thecosomes (Limacina helicina antarctica) and other mesozooplankton groups usually collected from 500 m depth during PS111 at the eastern Weddell Sea Shelf and the Filchner-Ronne ice shelf.