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 δ18O of ambient water, a feature potentially useful for reconstructing δ18O of local seawater. We report the first downcore δ18O 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 δ18O of ikaite crystals and hydration waters, we are able to infer local changes in fjord δ18O 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.

► Ikaite forms in a narrow and shallow zone. ► Natural crystal (in modern porewater) validates the fractionation factor from lab. ► Trends in ikaite δ18Ohydra and δ18OCaCO3 are comparable with other records. ► Ikaite record indicates that the influence of LIA and MWP reached the AP.