An ikaite record of late Holocene climate at the Antarctic Peninsula

Calcium carbonate can crystallize in a hydrated form as ikaite at low temperatures. The hydration water in ikaite grown in laboratory experiments records the δ ¹⁸O of ambient water, a feature potentially useful for reconstructing δ ¹⁸O of local seawater. We report the first downcore δ ¹⁸O record of natural ikaite hydration waters and crystals collected from the Antarctic Peninsula (AP), a region sensitive to climate fluctuations. We are able to establish the zone of ikaite formation within shallow sediments, based on porewater chemical and isotopic data. Having constrained the depth of ikaite formation and δ ¹⁸O of ikaite crystals and hydration waters, we are able to infer local changes in fjord δ ¹⁸O versus time during the late Holocene. This ikaite record qualitatively supports that both the Medieval Warm Period and Little Ice Age extended to the Antarctic Peninsula.