Palaeoclimatic implications of a storm erosion record from late Holocene lake sediments, North Island, New Zealand

A ca. 2250 year storm history has been identified from a high-resolution lake sediment record from the east coast of the North Island. New Zealand. This event-based chronology identifies 340 storms in the pre-European record. The record is largely one of natural variability without human impacts. Layers of minerogenic sediment representing the products of individual storm events are clearly visible in lake cores. These storm sediment pulses, derived mainly from landslides, record the frequency and magnitude of storms. Clusters of pulses identify six periods of high sedimentation and associated erosion before European settlement (A.D. 1878). At least five of these are interpreted as periods of higher rainfall and probably warmer temperatures, since historic records show that most large storms are derived from the subtropics/tropics. Most of the storm periods correspond to warm climate intervals previously identified from New Zealand and from Southern Hemisphere palaeoclimatic evidence. The Mapara 2 period (ca. 2090-1855 cal. yr B.P.) was the stormiest. Other periods were of shorter duration. The Mapara 2 period occurred at times of sustained warmth in the Tasmanian and Chilean tree-ring records, which might suggest hemispheric warming at this time. One storm period (Burrell), which occurred during the historical ENSO record, was at a time of moderately high ENSO activity. Three earlier periods also appear to show responses to ENSO. Two storm periods correspond to previously proposed New Zealand-wide periods of increased erosion and sedimentation. Estimates of palaeo-storm rainfalls from relationships between storm rainfall and sediment thickness of historical events suggest that storm pulses ca. 12 mm thick represent palaeo-storms of ca. 450 mm rainfall.