An evaluation of quantitative reconstruction of past precipitation records using coral skeletal Sr/Ca and delta O-18 data

[[abstract]]Coupled records of delta O-18 and Sr/Ca in Porites coral have been used to derive hydrological conditions by removing the Sr/Ca-inferred temperature component from the delta O-18 signal. Nanwan, a semi-enclosed bay in southern Taiwan, provides an opportunity to demonstrate the feasibility of quantitatively reconstructing past precipitation history. Recurrence of seawater delta O-18 offsets between wet and dry seasons in the early 1990s is well correlated with the precipitation record. Even though the hydrological signal only accounts for 20% of the total annual coral delta O-18 variation of ca. 1 parts per thousand, offsets can be found in the residual delta O-18 of modem corals after removing the thermal effect, which contributes to the other 80%. The observed timing and amplitude of the seasonal seawater delta O-18 offsets in Nanwan and their correlation with precipitation are reproduced by hydrological models. In the mid-Holocene, the seasonal anomaly of residual 5 180 was twice that of the modem value based on the 9-yr Sr/Ca-delta O-18 data recorded in a 6.73-ka Porites coral. Hydrological models suggest an annual rainfall of 1800-3000 mrn/yr at the window during mid-Holocene, 20% higher than that of the average of 30-yr modem instrumental records of 1500-2500 mm, consistent with the qualitative pollen record from lake sediments. The seasonal decrease of residual delta O-18 in 5 of 9 yr was earlier than the increase of the coral Sr/Ca-inferred temperature, which implies that these rainy seasons probably occurred from the early-mid-spring to mid-summer, earlier than that from late spring to late summer today. The driving force may be related to the changes of solar insolation and the East Asian monsoon. It is cautioned that the variability of hydrographic conditions imposes restrictions on a precise calculation of the amount of paleo-precipitation. The dynamic nature of local tectonics, monsoons and water circulation should be further addressed to precisely quantify precipitation over the past 10,000 yr from coral geochemical records. (c) 2005 Elsevier B.V. All rights reserved.[[fileno]]2010507010004[[department]]天文