A hydroclimate-proxy model based on sedimentary facies in an annually laminated sequence from Lake Ohau, South Island, New Zealand

Abstract

Annually laminated sediments collected from Lake Ohau, New Zealand offer an opportunity to generate a high-resolution paleoclimate record for the Southern Hemisphere mid-latitudes. Correlation between regional precipitation and synoptic climate indices like the Southern Annular Mode, paired with a correlation between Ohau catchment precipitation, lake inflow and suspended sediment yield suggest that the Lake Ohau varves are a potentially powerful tool for estimating the amplitude, timing and interdependence of different climate modes operating in the Southern Hemisphere mid-latitudes over time. A robust chronology and sound climate-proxy model are fundamental requirements for all high-resolution paleoenvironmental records. Here we present a chronology derived from layer counts, and 137Cs and 210Pb ages for the top 60 cm of sediments from the distal basin of Lake Ohau that confirm the varved natured of the sedimentary sequence. Sedimentary facies of different varve motifs are used to develop a hydroclimate-proxy model which links stratigraphy to seasonal hydrology. To establish this relationship we use a model accuracy statistic, which shows a quantitative difference between the annual hydrographs associated with each of three primary varve motifs. Distribution of above average inflow events points to summer and autumn hydrologic regimes as the primary control on the deposition of different motifs. This relationship between varve characteristics and hydrology will serve as a tool to reconstruct lake inflow, and by extension precipitation, on an annual basis throughout the late-Holocene for the South Island of New Zealand.