Palaeolimnological Records of Regime Shifts From Marine-To-Lacustrine System in a Coastal Antarctic Lake in Response to Post-Glacial Isostatic Uplift

Low altitude coastal lakes along the Antarctic margin often contain both marine and lacustrine sediments as a result of relative sea level changes due to deglaciation. The sediments also record changes in regional climate. A sediment core from a coastal lake in Larsemann Hills, East Antarctica, viz. Stepped Lake (Heart Lake), records distinct changes in C, N, C/N_{atomic ratio}, δ ¹³C_OM, δ ¹⁵N_OM and diatom abundance during the mid-Holocene (8.3 to 4.6 kyr BP). Lower values (C_org ~1%; C/N 8, ¹³C_OM ~ –18‰) during the early Holocene (8.3–4 kyr BP) are consistent with marine conditions, while higher values [C_org 6%; C/N 12; ¹³C_OM ~ –12‰) suggest a shift to lacustrine conditions (5.5–4.6 kyr BP). The diatom community shows similar shift with the major part of Holocene (8.3– 5.5 kyr BP) dominated by sea-ice and open-ocean diatoms while the core-top sections (5.5–4.6 kyr BP) transitions to lacustrine diatoms (Stauroforma inermis). These observations confirm that the basin was marine, and later became isolated as a result of postglacial isostatic uplift after 4.7 kyr BP.