(Table 1) Age determination of sediment cores CH07-98-22 and KNR140-2-59

Western subtropical North Atlantic oceanic and atmospheric circulations connect tropical and subpolar climates. Variations in these circulations can generate regional climate anomalies that are not reflected in Northern Hemisphere averages. Assessing the significance of anthropogenic climate change at regional scales requires proxy records that allow recent trends to be interpreted in the context of long-term regional variability. We present reconstructions of Gulf Stream sea surface temperature (SST) and hydrographic variability during the past two millennia based on the magnesium/calcium ratio and oxygen isotopic composition of planktic foraminifera preserved in two western subtropical North Atlantic sediment cores. Reconstructed SST suggests low-frequency variability of ~1°C during an interval that includes the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). A warm interval near 1250 A.D. is distinct from regional and hemispheric temperature, possibly reflecting regional variations in ocean-atmosphere heat flux associated with changes in atmospheric circulation (e.g., the North Atlantic Oscillation) or the Atlantic Meridional Overturning Circulation. Seawater d18O, which is marked by a fresher MCA and a more saline LIA, covaries with meridional migrations of the Atlantic Intertropical Convergence Zone. The northward advection of tropical salinity anomalies by mean surface currents provides a plausible mechanism linking Carolina Slope and tropical Atlantic hydrology.北大西洋西部亚热带海域的海洋与大气环流联结了热带与副极地气候系统。此类环流的变异可引发区域气候异常，而这类异常无法通过北半球平均气候记录体现。在区域尺度上评估人为气候变化的显著性，需要借助代用记录（proxy records），以将近期气候趋势置于长期区域变率的背景中进行解读。本研究基于两件北大西洋西部亚热带海域沉积物岩芯中保存的浮游有孔虫（planktic foraminifera）的镁钙比值与氧同位素组成，重建了过去两千年间湾流（Gulf Stream）海域的海表温度（SST）与水文变化。重建得到的海表温度显示，在涵盖中世纪气候异常期（MCA）与小冰期（LIA）的时段内，存在约1℃的低频变率。公元1250年前后的暖期与区域及半球温度变化存在显著差异，这可能反映了与大气环流（如北大西洋涛动（North Atlantic Oscillation））或大西洋经向翻转环流（Atlantic Meridional Overturning Circulation）变化相关的海-气热通量区域变异。海水d18O记录显示中世纪气候异常期偏淡、小冰期偏咸，其变化与大西洋热带辐合带（Atlantic Intertropical Convergence Zone）的经向迁移呈协变关系。平均表层洋流对热带盐度异常的北向平流，为联结卡罗来纳陆坡与热带大西洋水文状况提供了合理的物理机制。