Noon, Philippa Elizabeth; (1997) Recent environmental change at Signy Island, maritime Antarctic: Quantitative lake-sediment studies as a basis for reconstructing catchment ice-cover. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A quantitative reconstruction of recent environmental change at Signy Island (60°43'S, 45°38'W), maritime Antarctic, is performed using a model based on physical sediment characteristics. 20th Century climatic warming is the probable cause for recent deglaciation on Signy Island. Proxies in lake-sediments can be used to model the rates and directions of environmental change. Previous studies have made this link qualitatively. Here, a quantitative link is made between climate and lake-sediment response. The island's 17 freshwater lakes display different characteristics within a small geographical area. Multiple cores from each basin yielded 209 surface-sediment (0-1 cm) samples which were analyzed for their lithology, particle-size and mineral magnetism. Ordination and classification identify relationships between the sediment variables and the environmental factors responsible for within- and between-lake variability. Variance partitioning using a minimum adequate model of 14 significant environmental variables provides insights into the balance of limnological and catchment factors affecting overall sediment character and its component fractions. A portion of unexplained variance suggests that other unmeasured variables also play a role in determining sediment character. Catchment ice-cover is selected for reconstruction on the basis of its gradient length. An inverse regression model is constructed using four variables: % dry weight, % Loss On Ignition, mean particle-size and HARD%. Two methods of reconstruction - Partial Least Squares (PLS) Regression and analogue matching (MAT) are tested with various training-sets. Cross-validated prediction errors are ca. 13%, comparing favourably with historical (1968 AD) records. Calibration is performed at four sites using optimal models to reconstruct ice-cover. The model is a sensitive proxy for erosion. Reconstructions are compared with temperature records and affirm that climatic warming is the most likely cause for observed ice-retreat. Based on simple measures, the model could see application in similar locations in the Antarctic, Arctic and Alpine regions.

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