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/Natomic ratio, δ 13COM, δ 15NOM and diatom abundance during the mid-Holocene (8.3 to 4.6 kyr BP). Lower values (Corg ~1%; C/N 8, 13COM ~ -18‰) during the early Holocene (8.3-4 kyr BP) are consistent with marine conditions, while higher values [Corg 6%; C/N 12; 13COM ~ -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.
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