Reconnaissance sediment and microfossil analyses of a laminated short piston core from Lake Tekapo, South Island, New Zealand

Abstract

A 2.2 m piston core from the main basin of Lake Tekapo comprises millimetre‐centimetre‐scale alternations of light and dark laminae. Two much thicker layers occur near the base of the core and are interpreted as major slump deposits. Light laminae are predominantly fine silts with low microfossil concentrations. Dark laminae have higher clay, mica, and microfossil content and higher planktic/benthic diatom ratios. These findings are consistent with light laminae being deposited during times of high river flow and high sediment input, the thickness and number forming a proxy for paleoclimate (rainfall, water inflow, and erosion rates), and the dark laminae being deposited by settling out of the water column during periods of low inflow. The distribution of pollen from plants introduced to New Zealand by Europeans, and the inconsistency of dominant pollen types between samples, suggests that the entire sequence is only c. 100 yr old and that couplets of light and dark laminae form more frequently than annually. With appropriate processing, diatoms, spores, and pollen are present in great enough numbers in the dark laminae to be used for paleoclimate reconstruction. Diatoms are predominantly planktic lacustrine forms with some benthic forms sourced from the lake margins. Pollen and spores are derived from local grasslands, montane forest, fell fields, and tussock lands, and from West Coast lowland forest. Palynomorphs are carried over the central Southern Alps by prevailing northwesterly winds, and are deposited in the lake. The presence of fresh‐looking Casuarina and possibly Banksia and Eucalyptus pollen shows that it is likely that some pollen came from Australia. It is believed that the presence and abundance of West Coast derived pollen, particularly Dacrydium cupressinum, and to a lesser extent Ascarina lucida, Nothofagus, and Podocarpus/Prumnopitys species, could be used as a proxy for the intensity and persistence of northwesterly winds.