NOAA/WDS Paleoclimatology - Northwestern Subtropical Atlantic G. truncatulinoides Coiling Ratio Data over the past 280 kyr

We explore the use of the coiling direction of planktic foraminifer Globorotalia truncatulinoides in sediment cores from the northwestern subtropical Atlantic Ocean as a proxy for variations in the intensity of the western boundary of the subtropical gyre over the past 280 kyr. Core-top sediments from the study region are dominated by the left coiling variety consistent with the deep permanent thermocline at the study sites (KNR140-37PC and Ocean Drilling Program Site 1059). Down-core G. truncatulinoides (sinistral) maxima occur in conjunction with 14 out of the 25 (Northern and Southern Hemisphere) precession maxima contained in the study interval. The agreement between the dominance of left coiling tests and the precession index of the Southern Hemisphere, in particular, supports a link between a deep thermocline in the northwestern subtropical Atlantic and northward flow of equatorially-sourced warm surface currents, a situation analogues to the Late Holocene. Interglacial Marine Isotope Stage (MIS) 5 lacks G. truncatulinoides (s) minima attesting to the relative stability of the western boundary during an interval of prolonged global warmth. G. truncatulinoides (s) disappear during the glacial extremes of MIS 2, 6, and 8 implying a weaker western boundary current at these times. Our results support that the coiling direction of this species is sensitive to variations in hydrography of the western boundary of the subtropical gyre. Because of the association between G. truncatulinoides (s) and precession maxima in both hemispheres, results support the importance of oceanic heat transport in half-precession climate variability in the North Atlantic.

本研究探讨了利用亚热带西北大西洋海域沉积物岩芯中浮游有孔虫（planktic foraminifer）截圆辐格洛虫（Globorotalia truncatulinoides）的壳旋方向，作为重建过去28万年以来亚热带环流西边界强度变化的代用指标。研究区的表层沉积物以左旋型该种为主，这与研究站位（KNR140-37PC岩芯及大洋钻探计划（Ocean Drilling Program）1059站位）处的永久性深水温跃层特征相符。岩芯序列中截圆辐格洛虫（左旋型）的丰度峰值，与研究层位内25个（南北半球）岁差峰值中的14个相吻合。尤其是左旋壳体占优的特征与南半球岁差指数的一致性，佐证了亚热带西北大西洋深水温跃层与赤道来源暖表层洋流北向流动之间的关联，这一情形与全新世晚期相似。间冰期海洋同位素阶段（Marine Isotope Stage, MIS）5未出现截圆辐格洛虫（左旋型）的丰度谷值，表明在长期全球暖期内，亚热带环流西边界相对稳定。截圆辐格洛虫（左旋型）在MIS 2、6、8的冰期极盛期消失，暗示此时段西边界流强度较弱。本研究结果证实，该物种的壳旋方向对亚热带环流西边界的水文环境变化具有敏感性。鉴于截圆辐格洛虫（左旋型）与南北半球岁差峰值均存在关联，本研究结果支持海洋热输送在北大西洋半岁差气候变率中的重要作用。