The seabed distributions of labile organic carbon (LOC), i.e., recently produced organic matter from marine plankton, were studied under the former Larsen A Ice Shelf using the naturally occurring radioisotopes, ¹⁴C and ²¹⁰Pb. Samples were collected along an East-West transect at 5 stations representing the ice-shelf edge at different times during retreat over the past 170 years, creating a spatial time series in the sampling scheme. The effects of bioturbation on LOC characteristics were assessed using a non-steady-state model to generate LOC degradation coefficients and turnover times. Based on non-steady-state ²¹⁰Pb profiles, mixing coefficients ranged from 0.5 cm²/y to 5 cm²/y. The seabed inventory of LOC decreased towards the current ice-shelf edge from 75 mg/cm² to 10 mg/cm². The depth of LOC penetration into the seabed varied from 20 cm in the eastern stations (oldest bioturbated regime) to 8 cm in the western stations (youngest bioturbated regime). LOC turnover times ranged from 60y to 6y, with lower values typically at the current ice-shelf edge. Trends in turnover time suggest that the LOC component of bulk organic matter is becoming less reactive and aging with time since overlying ice-shelf retreat.