Williams, P.W., King, D.N.T., Zhao, J.-X. and Collerson, K.D. 2004. Speleothem master chronologies: combined Holocene 18O and 13C records from the North Island of New Zealand and their palaeoenvironmental interpretation. The Holocene 14: 194-208.
Temperatures were inferred from δ18O data obtained from four stalagmites found in caves at Waitomo (38.3°S, 175.1°E) on New Zealand's North Island for which 19 TIMS uranium series ages were measured. The Medieval Warm Period occurred between AD 1100 and 1400 and was warmer than the Current Warm Period.