A Coupled Calibration and Modelling Approach to the Understanding of Dry-Land Lake Oxygen Isotope Records

Matthew D Jones,Murat Türkeş,C Neil Roberts,Melanie J Leng,Rana Moyeed

doi:10.1007/s10933-005-6743-0

Abstract

Comparisons between climate proxies and instrumental records through the last two centuries are often used to understand better the controls on palaeoarchives and to find relationships that can be used to quantify changes in pre-instrumental climate. Here we compare an 80-year-long annually resolved oxygen isotope record from Nar Golu, Turkey, a varved lake sequence, with instrumental records of temperature, precipitation, wind speed, relative humidity and calculated values of evaporation, all of which are known to be possible controls on lake oxygen isotope systems. Significant relationships are found between the isotope record and summer temperatures and evaporation suggesting these are dominant controls on the isotope hydrology of this non-outlet lake. Modelling the stable isotope hydrology of the lake system allows these relationships to be tested independently. We show that the isotope record follows the same trends in the temperature and evaporation records but that, even when combined, these two climatic factors cannot fully explain the magnitude of change observed in the isotope record. The models show the lake system is much less sensitive to changes in evaporation and temperature than the climate calibration suggests. Additional factors, including changes in the amount of precipitation, are required to amplify the isotope change. It is concluded that proxy-climate calibrations may incorrectly estimate the amplitude of past changes in individual climate parameters, unless validated independently.

Highlights

A coupled calibration and modelling approach to the understanding of dry-land lake oxygen isotope records
This study has shown statistically significant relationships between a non-outlet lake δ18O record measured on annual carbonate varves and summer drought intensity derived from historic meteorological records, summer evaporation and temperature
The calibration overestimates the sensitivity of the δ18O system to changes in evaporation and the model cannot explain the recorded carbonate δ18O by using changes in temperature and evaporation alone

Summary

Introduction

A coupled calibration and modelling approach to the understanding of dry-land lake oxygen isotope records. For records of palaeoclimatic change to be useful to climate modellers, and to put the recorded climate variability through the last century into context, it is necessary to try and quantify records of past change This requires understanding of the modern processes controlling the palaeoarchive. It requires testing of the assumption that these controls have not changed significantly through time or, if they have, that changes can be sufficiently accounted for This is important when trying to quantify changes in climate from lake oxygen isotope records as there are many factors that control lake stable-isotope values (Leng and Marshall 2004).

Methods

Findings

Conclusion