A stable isotope record for Lake Poukawa, Hawkes Bay, New Zealand

Abstract

Climatic and environmental changes during the last 100 ka are inferred from stable isotope (δ18O and δ13C) records obtained from the sediments of Lake Poukawa, Hawkes Bay, New Zealand. Comparison of isotopic records obtained on mollusc shells, marl, and whole sediment samples supports estimates of relative changes in both lake water and mean annual air temperatures. The combined modern carbonate and water isotopic record can be used as a proxy for paleoenvironmental analysis of ancient sediments in Lake Poukawa. The isotope record of the modern water has been used to help constrain the temperature of carbonate precipitation of the marl and shells in the ancient sediments. Isotopic shifts indicate climatic changes, and are congruent with variations in the other multiproxy records. Variations in lake dynamics (productivity, topography, and hydrology) and external conditions (air temperature, precipitation, tectonics and erosion) are indirectly recorded in the isotopic signature of the carbonates. Marine Isotope Stages 1 to 5 have been identified in the core on the basis of vegetation and microfaunal evidence and are clearly supported by the stable isotope record. The variation in climate during these stages can be assessed by using the relationship between the isotopic record and the precipitation of carbonates, providing estimates for lake water temperatures and mean annual air temperatures.