Stable isotope record and aklenonen index of MIS 11 sediments

The interglacial known as Marine Isotope Stage 11 has been proposed to be analogous to the Holocene, owing to similarities in the amplitudes of orbital forcing. It has been difficult to compare the periods, however, because of the long duration of Stage 11 and a lack of detailed knowledge of any extreme climate events that may have occurred. Here we use the distinctive phasing between seasurface temperatures and the oxygen-isotope records of benthic foraminifera in the southeast Atlantic Ocean to stratigraphically align the Holocene interglacial with the first half of the Marine Isotope Stage 11 interglacial optimum. This alignment suggests that the second half of Marine Isotope Stage 11 should not be used as a reference for 'pre-anthropogenic' greenhouse-gas emissions. By compiling benthic carbon-isotope records from sites in the Atlantic Ocean on a single timescale, we also find that meridional overturning circulation strengthened about 415,000 years ago, at a time of high orbital obliquity. We propose that this mechanism transported heat to the high northern latitudes, inhibiting significant ice-sheet build-up and prolonging interglacial conditions. We suggest that this mechanism may have also prolonged other interglacial periods throughout the past 800,000 years.

被称为海洋同位素阶段11（Marine Isotope Stage 11）的间冰期，因轨道强迫振幅特征与全新世（Holocene）高度相似，曾被认为与全新世间冰期具有可比性。然而，由于海洋同位素阶段11持续时长较长，且对其期间可能发生的极端气候事件缺乏详尽认知，学界此前难以对这两个间冰期开展对比研究。本文借助东南大西洋海域海表温度（seasurface temperatures）与底栖有孔虫（benthic foraminifera）氧同位素记录（oxygen-isotope records）之间独特的相位关系，将全新世间冰期与海洋同位素阶段11间冰期最佳期的前半段进行地层学对齐。该对齐结果显示，海洋同位素阶段11的后半段不应被用作“人类活动前”温室气体排放的参照基准。通过将大西洋海域各站位的底栖碳同位素记录整合至统一年代标尺，本文还发现，在轨道倾角（orbital obliquity）偏高的约41.5万年前，经向翻转环流（meridional overturning circulation）出现增强。本文提出，该环流机制将热量输送至高北纬地区，抑制了大规模冰盖的发育，从而延长了间冰期环境的持续时长。本文认为，该机制或许同样延长了过去80万年间的其他间冰期时段。