NOAA/WDS Paleoclimatology - Florida Straits 20KYr Mg/Ca SST and d18Osw Reconstructions

The prevailing paradigm of abrupt climate change holds that rapid shifts associated with the most extreme climate swings of the last glacial cycle were forced by changes in the strength and northward extension of Atlantic Meridional Overturning Circulation (AMOC), resulting in an abrupt reorganization of atmospheric circulation patterns with global teleconnections. To determine the timing of tropical Atlantic atmospheric circulation changes over the past 21 ka BP, we reconstruct high resolution sea surface temperature and d18OSW (a proxy for surface salinity) records based on Mg/Ca ratios and oxygen isotope measurements in the planktonic foraminifera Globigerinoides ruber from a sediment core located on the western margin of the Florida Straits. As a proxy for meltwater discharge influence on Florida Straits surface water salinity, we also measured Ba/Ca ratios in G. ruber from the same core. Results show that riverine influence on Florida Straits surface water started by 17.2 ka BP and ended by 13.6 ka BP, 600 years before the start of the Younger Dryas (YD) cold interval. The initiation of the YD is marked by an abrupt increase in Florida Straits d18OSW values, indicating a shift to elevated sea surface salinity occurring in 130 years, most likely resulting from increased regional aridity and/or reduced precipitation. In order to resolve the timing of tropical atmospheric circulation change relative to AMOC variability across this transition, we compare the timing of surface water changes to a recently published record of Florida Current variability in the same core reconstructed from benthic oxygen isotope measurements. We find synchronous changes in atmospheric and ocean circulation on the transition into the YD, consistent with an abrupt reduction in AMOC as the driver of tropical Atlantic atmospheric circulation change at this time.当前主流的突发性气候变化学术范式认为，末次冰期旋回中与极端气候波动相关的快速气候跃迁，由大西洋经向翻转环流（Atlantic Meridional Overturning Circulation, AMOC）的强度变化及其北向扩张所驱动，进而引发大气环流格局发生突发性重组，并产生全球性遥相关效应。为确定过去21 ka BP（距今21000年）间热带大西洋大气环流变化的时间节点，我们基于取自佛罗里达海峡西部边缘一处沉积岩芯中的浮游有孔虫红拟抱球虫（Globigerinoides ruber）的镁钙比值与氧同位素实测数据，重建了高分辨率海表温度及d18OSW（表层盐度代用指标）记录。作为衡量融水排放对佛罗里达海峡表层水盐度影响的代用指标，我们还测定了同一岩芯中G. ruber的钡钙比值。研究结果显示，河流作用对佛罗里达海峡表层水的影响始于17.2 ka BP，终止于13.6 ka BP，较新仙女木（Younger Dryas, YD）冷期的起始时间早600年。新仙女木期的启动以佛罗里达海峡d18OSW值的突发性升高为标志，表明海表盐度在130年内快速上升，这一变化极有可能由区域干旱加剧和/或降水减少所引发。为厘清此次气候转型期间热带大气环流变化相对于AMOC变率的时间序列，我们将表层水变化的时间节点与一项新近发表的、基于同一岩芯底栖氧同位素重建的佛罗里达流变率记录进行了对比。我们发现，在向新仙女木期转型的过程中，大气环流与海洋环流发生同步变化，这与AMOC突发性减弱是当时热带大西洋大气环流变化驱动因子的结论相一致。