Sea-surface temperature reconstructions over 30-40 ka, supplement data to Jensen et al. 2018@en

Here we establish a spatio-temporal evolution of the sea-surface temperatures in the North Atlantic over Dansgaard-Oeschger (DO) events 5-8 (c.30-40ka) using the proxy surrogate reconstruction method. Proxy data suggest a large variability in North Atlantic sea-surface temperatures during the DO-events of the last glacial period. However, proxy data availability is limited and cannot provide a full spatial picture of the oceanic changes. Therefore, we combine fully coupled, general circulation model simulations with planktic foraminifera based sea-surface temperature reconstructions to obtain a broader spatial picture of the ocean state during DO-events 5-8. The resulting spatial sea-surface temperature patterns agree over a number of different general circulation models and simulations. We find that sea-surface temperature variability over the DO-events is characterized by colder conditions in the subpolar North Atlantic during stadials than during interstadials, and the variability is linked to changes in the Atlantic Meridional Overturning circulation, and in the sea-ice cover. Forced simulations are needed to capture the strength of the temperature variability and to reconstruct the variability in other climatic records not directly linked to the sea-surface temperature reconstructions. This is the first time the proxy surrogate reconstruction method has been applied to oceanic variability during MIS3. Our results remain robust, even when age uncertainties of proxy data, the number of available temperature reconstructions, and different climate models, are considered. However, we also highlight shortcomings of the methodology that should be addressed in future implementations.本研究采用代用指标替代重建法（proxy surrogate reconstruction method），重建了末次冰期丹斯果-奥什格尔（Dansgaard-Oeschger, DO）5-8号事件（约30~40 ka）期间北大西洋海表温度的时空演化过程。代用指标数据显示，末次冰期DO事件期间，北大西洋海表温度存在显著波动。但代用指标数据的可获取性有限，无法完整呈现海洋变化的空间分布特征。为此，本研究将完全耦合的大气环流模式（general circulation model, GCM）模拟结果与基于浮游有孔虫（planktic foraminifera）的海表温度重建数据相结合，以获取DO 5-8事件期间海洋状态更完整的空间图景。所得的海表温度空间分布型在多组不同的大气环流模式及模拟试验中均表现一致。研究发现，DO事件期间的海表温度波动表现为：亚极地北大西洋在冰阶（stadial）时期的温度显著低于间冰阶（interstadial）时期；且该波动与大西洋经向翻转环流（Atlantic Meridional Overturning Circulation, AMOC）以及海冰覆盖的变化密切相关。若要还原温度波动的幅度，并重建与海表温度重建无直接关联的其他气候记录中的波动特征，则需要开展强迫模拟试验。本研究首次将代用指标替代重建法应用于深海氧同位素3期（Marine Isotope Stage 3, MIS3）期间的海洋波动研究。即便在考虑代用指标数据的年代不确定性、可用温度重建数据的数量以及不同气候模式的差异时，本研究结果仍保持稳健。但本研究同时指出了该方法存在的不足，有待在未来的研究中予以改进。