El Niño–Southern Oscillation variability recorded in estuarine sediments of the Changjiang River, China

Abstract

El Niño–Southern Oscillation (ENSO) has a strong influence on the climate of the Changjiang River basin, China, most notably upon extreme events such as flooding and drought. However, long-term historical records, which reveal the impacts of ENSO variability on climatic and environmental changes in this region, are scarce. A sediment core (G9) was collected from the estuarine delta of the Changjiang River. And its elemental ratios, mineral compositions, and grain size distribution were analyzed to investigate the links between sediment parameters in this region and the history of ENSO variability during the last century. Observed variations in K2O/Na2O, Al2O3/SiO2, and Rb/Sr ratios are synchronous with changes in mineral compositions and grain size throughout the sediment core. Lower K2O/Na2O, Al2O3/SiO2, and Rb/Sr ratios generally correspond to lower ratios of clay minerals to rock-forming minerals and larger grain sizes, which in turn correspond to periods of flooding in the Changjiang River basin. Such trends probably reflect increased physical erosion and the transport of greater amounts of coarse-grained suspended matter to the estuary. These geochemical proxies are also positively correlated with sea surface temperature anomalies in the Niño-3.4 region (120°W–170°W, 5°S–5°N) (using a low-pass filter with a cut-off of 13 years). We therefore conclude that (1) ENSO-related flood events in the Changjiang River basin have a strong influence on physical erosion processes in the upper catchment area and thereby influence the grain size distribution, elemental ratios, and mineral compositions of the estuarine sediments; and (2) the geochemical records presented here can serve as a proxy for ENSO-driven regional weathering variations on decadal to centennial time scales, because they could potentially be recorded in longer sediment cores recovered from the Changjiang River estuary.