δ(13)C-δ(18)O covariance: an effective indicator of hydrological closure for lakes?

Abstract

The correlation between the δ13 C and δ18 0 in primary carbonates is affected by several factors such as hydrological balance, total CO2 concentrations, climatic condition and lake productivity. The influence of these factors on the δ13 C-δ18 0 correlation may be different on different time scales. In this paper, two different-type lakes in southwestern China, Lake Erhai and Lake Chenghai, are selected to investigate the influence of climatic pattern on the δ13 C-δ18 0 correlation and to evaluate the reliability of the δ13 C-δ18 0 covariance as an indicator of hydrological closure. The results show that there exists good correlation between the δ13 C and δ18 0 in Lake Erhai (overflowing open lake) and in Lake Chenghai (closed lake). This suggests that the δ13 C-δ18 0 covariance may be not an effective indicator of hydrological closure for lakes, especially on short time scales. On the one hand, a hydrologically open lake may display covariant δ13 C and δ18 0 as a result of climatic influence. The particular alternate warm-dry and cold-wet climatic pattern in southwestern China may be the principal cause of the δ13 C-δ18 0 covariance in Lake Erhai and Lake Chenghai. On the other hand, a hydrologically closed lake unnecessarily displays covariant trends between δ13 C and δ18 O because of the buffering effect of high CO2 concentration on the δ13 C shift in hyper-alkaline lakes. We should be prudent when we use the covariance between δ13 C and δ18 O to judge the hydrological closure of lake.