Last Millennium Meridional Shifts in Hydroclimate in the Central Tropical Pacific

Reconstructing past changes in the spatial structure of tropical Pacific hydroclimate requires archives of past moisture balance across spatial gradients of precipitation. To date, only one, 600-year, terrestrial record of hydroclimate is available for the central tropical Pacific (CTP) from Washington Lake, Washington Island, limiting the ability to test the hypotheses regarding the location of the CTP Intertropical Convergence Zone (ITCZ) in the last millennium. A new lake sediment record from Lake 30, Kiritimati, Republic of Kiribati, 3° south of Washington Island, provides additional constraints on past CTP ITCZ position. Lake 30 geochemical and sedimentological data indicate an episode of increased microbial mat development and gypsum precipitation from 900 to 1200 CE, coincident with the Medieval Climate Anomaly (MCA). We infer drier conditions during the MCA at Kiritimati as the Washington Lake proxy record indicates wetter conditions, suggesting that the CTP ITCZ was displaced northward during the MCA relative to its position today. At the transition between the MCA and the Little Ice Age (LIA), Lake 30 sediment becomes predominantly carbonate, suggesting a transition to wetter conditions and a southward shift of the ITCZ relative to its MCA position. However, a tropical Pacific synthesis of hydroclimate-sensitive proxy records does not point to a consistent spatial or temporal pattern of variability in the MCA and LIA, suggesting multiple influences on centennial-scale tropical Pacific hydroclimate during the last millennium.