(Table S1) Age determination of sediment cores of the Azores Current System

In order to test the sensitivity of marine primary productivity in the midlatitude open ocean North Atlantic to changes in the Atlantic Meridional Overturning Circulation (AMOC), we investigated two spliced sediment cores from a site south of the Azores Islands at the northern rim of the North Atlantic subtropical gyre. For this purpose we analyzed coccolithophore assemblages, diatom abundances, alkenones and conducted X-ray fluorescence (XRF) core scanning. During times of reduced AMOC, especially during Heinrich event 1 (H1) and the Younger Dryas, we observe a strong increase in productivity as evidenced by high coccolith accumulation rates, high alkenone concentrations/accumulation rates, high Ba/Ti-ratios, high abundances of diatoms and low abundances ofF. profunda. The increased productivity is partly caused by a more southern position of the Azores Front (AzF), and hence by a less northward extension of the subtropical gyre, as deduced from high abundances of the temperate coccolithophore species G. muellerae and low abundances of subtropical species (Oolithotus spp., Umbellosphaera spp., Umbilicosphaeraspp.). However, to explain the full range of the observed productivity increase, other factors like increased westerly winds and advection of nutrient-rich surface waters have also to be considered. Because this pattern can also be observed in other sediment cores from the midlatitude North Atlantic, we propose that during times of reduced AMOC there has been a band of strongly increased productivity across the North Atlantic at the northern rim of the contracted subtropical gyre, which partly counteracts the decreased organic carbon pump in the high northern latitudes.

为检验北大西洋中纬度开阔海域海洋初级生产力对大西洋经向翻转环流（Atlantic Meridional Overturning Circulation, AMOC）变化的敏感性，我们于北大西洋亚热带环流圈北缘亚速尔群岛南部海域采集了两根拼接沉积岩芯开展研究。为此，我们分析了颗石藻群落组成、硅藻丰度、烯酮类化合物，并开展了X射线荧光（XRF）岩芯扫描。在AMOC减弱的时期，尤其是海因里希事件1（Heinrich event 1, H1）和新仙女木期，我们观测到生产力显著升高，该现象可通过以下指标佐证：高颗石藻堆积速率、高烯酮浓度/堆积速率、高钡钛比值、高硅藻丰度以及低深居弗氏颗石藻（F. profunda）丰度。生产力升高的部分诱因是亚速尔锋面（Azores Front, AzF）位置向南偏移，即亚热带环流圈北伸范围缩小，这一推论可由温带颗石藻物种穆勒氏桥石藻（G. muellerae）的高丰度，以及亚热带类群（石囊颗石藻属Oolithotus spp.、伞球颗石藻属Umbellosphaera spp.、脐球颗石藻属Umbilicosphaera spp.）的低丰度得到印证。然而，要完整解释观测到的生产力升高幅度，还需纳入其他影响因素，例如增强的西风以及营养盐富集表层水的平流输送。由于该变化模式在北大西洋中纬度其他沉积岩芯中均有观测记录，我们提出：在AMOC减弱时期，收缩的亚热带环流圈北缘横跨北大西洋形成了一条生产力显著升高的带状区域，该区域在一定程度上抵消了高纬度北大西洋有机碳泵的减弱效应。