Temporal Evolution and Origin of Radionuclide Fallout and Contaminants Recorded in Sediment from the Kerguelen Archipelago Fjord System

Deposition of heavy metals and persistent organic pollutants (POPs) in fjord systems during ice melting was investigated with a sediment core collected in Table Fjord from Kerguelen Island (49° 33.8 S-69° 13.9 E) situated in the Southern Indian Ocean. Multiple radionuclides (²¹⁰Pb_ex, ¹³⁷Cs, ²⁴⁰Pu/²³⁹Pu) were used to establish an accurate age-depth model and show the occurrence of French nuclear weapon test fallout in this remote region for the first time. Environmental changes related to the retreat of the Cook Ice Cap since the 1960s were found to be one of the major factors dominating the dynamics of anthropogenic lead deposition flux in the fjord through the release of long-range transported legacy anthropogenic lead. The released legacy anthropogenic lead was likely transported across the proglacial Ampere Lake by a hypopycnal plume to the fjord. Backward trajectories and lead stable isotopic signatures suggest the southern part of South Africa as a major source of anthropogenic lead transported to the Kerguelen Archipelago. In contrast, contamination by arsenic, molybdenum, antimony, and POPs was found to be more recent (since 2001). Fractionation of rare earth elements was observed in the sediment due to the formation of proglacial Ampere Lake, which acts as a sediment trap.