Late Miocene and Pliocene dinoflagellate cysts, acritarchs and terrestrial palynomorphs from ODP Hole 642B, Vøring Plateau, Norwegian Sea

The globally warm climate of the early Pliocene gradually cooled from 4 million years ago, synchronous with decreasing atmospheric CO2 concentrations. In contrast, palaeoceanographic records indicate that the Nordic Seas cooled during the earliest Pliocene, before global cooling. However, a lack of knowledge regarding the precise timing of Nordic Seas cooling has limited our understanding of the governing mechanisms. Here, using marine palynology, we show that cooling in the Nordic Seas was coincident with the first trans-Arctic migration of cool-water Pacific mollusks around 4.5 million years ago, and followed by the development of a modern-like Nordic Seas surface circulation. Nordic Seas cooling precedes global cooling by 500,000 years; as such, we propose that reconfiguration of the Bering Strait and Central American Seaway triggered the development of a modern circulation in the Nordic Seas, which is essential for North Atlantic Deep Water formation and a precursor for more widespread Greenland glaciation in the late Pliocene.

上新世（Pliocene）早期的全球温暖气候自400万年前起逐渐降温，这一过程与大气二氧化碳（CO₂）浓度的持续下降同步发生。与之形成对比的是，古海洋学（palaeoceanography）记录显示，挪威海（Nordic Seas）在全球降温之前的上新世早期就已出现降温现象。然而，学界对挪威海降温的确切时间节点缺乏精准认知，这限制了我们对其背后主导机制的理解。本研究借助海洋孢粉学（marine palynology）分析手段证实，挪威海的降温与约450万年前冷水型太平洋软体动物首次完成跨北极迁徙（trans-Arctic migration）的时间完全吻合，且此后挪威海表层环流逐步形成类似现代的格局。挪威海降温比全球降温早50万年；据此我们提出，白令海峡（Bering Strait）与中美洲海道（Central American Seaway）的重构触发了挪威海现代环流的形成——这一环流对北大西洋深层水（North Atlantic Deep Water）的形成至关重要，同时也是上新世晚期格陵兰冰盖发育（Greenland glaciation）的前置条件。