The Plenus Cold Event (PCE) temporarily interrupted the supergreenhouse conditions exacerbated during much of the Cenomanian–Turonian Oceanic Anoxic Event 2 (OAE 2). The PCE is coeval to the occurrence of Boreal benthic macroinvertebrates and of the nektonic belemnite Praeactinocamax plenus (after which the event is named) in Europe, and to the re-oxygenation of bottom waters in the Northern Hemisphere. However, its effects on the sea-surface circulation are unknown and evidence for changes in the biogeography of planktonic organisms are limited to the equatorward migration of the dinoflagellate cysts grouped in the Cyclonephelium compactum–membraniphorum morphological plexus.

This study presents new planktonic foraminiferal quantitative data from two complete OAE 2 records of the Anglo-Paris (Eastbourne, SE England) and Vocontian (Clot Chevalier, SE France) basins that registered the equatorward pulse of Boreal macroinvertebrates during the PCE and have been extensively studied for bio- and chemostratigraphy.

At the onset of OAE 2 (before the PCE), planktonic foraminifera are mainly represented by oligo-mesotrophic Tethyan taxa (rotaliporids and whiteinellids) in both localities, but this assemblage is sharply replaced by cold and meso-to-eutrophic species (praeglobotruncanids, dicarinellids and muricohedbergellids) during the PCE. The cold-water assemblage shows strong affinities with the coeval fauna of the Norwegian Sea and yields the Boreal endemic species Muricohedbergella kyphoma and Praeglobotruncana plenusiensis. This observation combined with previously published data collected in other localities of the Northern Hemisphere and on other fossil groups suggests a ~20° equatorward expansion of the Boreal marine bioprovince during the PCE. Moreover, contrarily to the nektonic belemnitellids that were able to move independently of ocean circulation, planktonic organisms are passively transported by currents and changes in the planktonic foraminiferal assemblages documented in the Anglo-Paris and Vocontian basins have been interpreted to reflect the transition from a dominant influence of warm, saline, and thermally stratified waters carried by the proto-Gulf Stream before the PCE to cold and low-saline Boreal waters originated in the Norwegian Sea during the PCE. We suggest that such changes were forced by the equatorward shift of the proto-Arctic Front (i.e., the boundary between warm saline Tethyan-Atlantic and cold low-saline Boreal waters) from offshore Norway to Southern England. In this southerly position, the proto-Arctic Front represented an oceanographic barrier that limited the influence of the proto-Gulf Stream in the Anglo-Paris Basin, and favored the inflow of Boreal waters from the North to the European epicontinental basins.

The sea-surface cooling and equatorward expansion of Boreal planktonic assemblages during the PCE are of the same order of magnitude of those reconstructed between some glacial and interglacial intervals of the Plio-Pleistocene. Despite obvious differences between Cretaceous and Plio-Pleistocene paleogeography and climate dynamics, this study reviews the extent of environmental changes occurred during the PCE, provides evidence for a profound re-organization of the sea-surface circulation patterns and a more comprehensive overview of the equatorward migration of Boreal marine communities in the Northern Hemisphere.

Plenus 冷事件 (PCE) 暂时中断了在 Cenomanian-Turonian 海洋缺氧事件 2 (OAE 2) 的大部分时间里加剧的超级温室条件。PCE 与欧洲底栖大型无脊椎动物和游动箭石Praeactinocamax plenus（以该事件命名）以及北半球底水的再充氧同时发生。然而，它对海面环流的影响是未知的，浮游生物生物地理学变化的证据仅限于聚集在紧致旋风-膜藻形态丛中的甲藻囊肿向赤道迁移。

本研究提供了来自盎格鲁-巴黎（伊斯特本，英格兰东南部）和 Vocontian（Clot Chevalier，法国东南部）盆地的两个完整 OAE 2 记录的新浮游有孔虫定量数据，这些记录记录了 PCE 期间北方大型无脊椎动物的赤道脉冲，并已被广泛研究生物地层学和化学地层学。

在 OAE 2 开始时（PCE 之前），浮游有孔虫主要由两个地方的寡中营养特提斯类群（轮状孔纲和白线纲）代表，但这种组合被冷和中至富营养化的物种（原球藻、 dicarinellids 和 muricohedbergellids）在 PCE 期间。冷水组合与挪威海的同时代动物群表现出很强的亲和力，并产生了北方特有物种Muricohedbergella kyphoma和Praeglobotruncana plenusiensis. 这一观察结果与之前在北半球其他地区和其他化石群中收集的先前公布的数据相结合，表明在 PCE 期间，北方海洋生物省向赤道方向扩张了约 20°。此外，与能够独立于海洋环流而移动的游动剑类相反，浮游生物通过洋流被动运输，并且在盎格鲁-巴黎和沃康蒂盆地中记录的浮游有孔虫组合的变化被解释为反映了从占主导地位的过渡PCE 之前原始墨西哥湾流携带的温暖、咸水和热分层水对 PCE 期间起源于挪威海的寒冷和低盐度北方水域的影响。我们认为这种变化是由原始北极锋向赤道移动（即 ，温暖的咸特提斯大西洋和寒冷的低盐度北方水域之间的边界）从挪威近海到英格兰南部。在这个向南的位置，原北极锋代表了一个海洋屏障，它限制了盎格鲁-巴黎盆地中原墨西哥湾流的影响，并有利于北方水域从北方流入欧洲大陆表盆地。

PCE期间北方浮游组合的海面冷却和赤道扩张与上新世某些冰川和间冰期之间重建的那些具有相同的数量级。尽管白垩纪和上新世-更新世古地理和气候动力学之间存在明显差异，但本研究回顾了 PCE 期间发生的环境变化程度，为海面环流模式的深刻重组和更全面的赤道地区概况提供了证据。北半球北方海洋群落的迁移。