A diatom-based reconstruction of summer sea-surface salinity in the Southern Okinawa Trough, East China Sea, over the last millennium

摘要

A high-resolution diatom record from site MD05-2908 in the Southern Okinawa Trough, East China Sea, reveals pronounced multidecadal- to centennial-scale palaeoceanographic changes throughout the last millennium. Summer sea-surface salinity (SSS) was reconstructed using a weighted averaging partial least squares diatom-based training set. The reconstructed SSS shows slightly decreasing values during the period AD 905-1930 with considerable fluctuations superimposed on this general trend. Relatively high-salinity conditions during the interval AD 905-1450 probably suggest a low flood frequency in north-eastern Taiwan. Furthermore, the high SSS values are associated with a strong and stable influence of the Kuroshio Current on the Southern Okinawa Trough during the Medieval Climate Anomaly. The period AD 1450-1930 is characterized by three low-salinity intervals (AD 1450-1500, AD 1625-1725 and AD 1770-1880) separated by periods of relatively high salinity. The low SSS intervals indicate increased freshwater discharge into the Southern Okinawa Trough during the Little Ice Age, probably as a result of higher flood frequencies in north-eastern Taiwan. Spectral and wavelet analyses suggest that this pattern was linked to multidecadal variations in summer SSS, presumably associated with the Pacific Decadal Oscillation.