Sr/Ca, U/Ca, and stable isotope data and bimonthly records of Ogasawara coral core OGA-02-1

Instrumental climate observations provide robust records of global land and ocean temperatures during the twentieth century. Unlike for temperature, continuous salinity observations in the surface ocean are scarce prior to 1970, and the magnitude of salinity changes during the twentieth century is largely unknown. Surface ocean salinity is a major component in climate dynamics, as it influences ocean circulation and water mass formation. Here we present an annually resolved reconstruction of salinity variations in the surface waters of the western subtropical North Pacific Ocean since 1873, based on bimonthly records of d18O, Sr/Ca, and U/Ca in a coral from the Ogasawara Islands. The reconstruction indicates that an abrupt regime shift toward fresher surface ocean conditions occurred between 1905 and 1910. Observational atmospheric data suggest that the abrupt freshening was associated with a weakening of the winds that drive the Kuroshio Current system and the associated subtropical gyre circulation. We note that the abrupt early-twentieth-century freshening in the western subtropical North Pacific precedes abrupt climate change in the northern North Atlantic by a few years. The potential for abrupt regime shifts in surface ocean salinity should be considered in climate predictions for the coming decades.

器测气候观测为20世纪全球陆地与海洋温度提供了可靠的记录。与温度观测不同，1970年之前表层海洋的连续盐度监测资料十分匮乏，20世纪盐度变化的幅度在很大程度上尚不明确。表层海洋盐度是气候动力学的核心组成部分，因其可影响海洋环流与水团形成。本研究基于小笠原群岛（Ogasawara Islands）一份珊瑚样品的双月δ¹⁸O（d18O）、锶钙比（Sr/Ca）与铀钙比（U/Ca）观测记录，重建了1873年以来北太平洋西部亚热带海域表层水盐度变化的年分辨率序列。该重建结果显示，1905年至1910年间，该海域表层海洋环境发生了向低盐态方向的突变型态转换。大气观测资料表明，此次盐度突降与驱动黑潮（Kuroshio Current）体系及相关亚热带环流的风力减弱存在关联。我们注意到，北太平洋西部亚热带海域20世纪早期的盐度突降，较北大西洋北部的突变型气候转变早数年发生。在未来数十年的气候预测工作中，应当充分考虑表层海洋盐度发生突变型态转换的潜在可能性。