Abstract. It has been hypothesized that global temperature trends are tightly linked to tropical thermocline depth, and that thermocline shoaling played a crucial role in the intensification of late Pliocene northern hemisphere glaciation. The Pliocene thermocline evolution in the Pacific Ocean is well documented and supports this hypothesis, but thermocline records from the tropical Atlantic Ocean are limited. We present new planktonic foraminiferal Mg/Ca, δ¹⁸O and δ¹³C records from the late Pliocene interval at Ocean Drilling Program Site 959 in the eastern equatorial Atlantic (EEA), which we use to reconstruct ocean temperatures and relative changes in salinity and thermocline depth. Data were generated using surface-dwelling Globigerinoides ruber and subsurface-dwelling Neogloboquadrina dutertrei. Reduced gradients between the surface and subsurface records indicate deepening of the EEA thermocline at the end of the Mid-Piacenzian Warm Period (mPWP; ~3.3–3.0 Ma). We connect our late Pliocene records to previously published early Pliocene δ¹⁸O data from Site 959 and compare these to the Site 1000 in the Caribbean Sea. Over the course of the Pliocene, thermocline changes in the EEA and Caribbean Sea follow similar patterns, with prominent step-wise thermocline deepening between ~5.5 and 4.0 Ma, gradual shoaling up to the mPWP, followed by minor deepening at the end of the mPWP. The tropical thermocline depth evolution of the tropical Atlantic differs from the Pacific, which is characterized by gradual basin-wide shoaling across the Pliocene. These results potentially challenge the hypothesized link between tropical thermocline depth and global climate. The mechanisms behind the periodically divergent Pacific and Atlantic thermocline movements remain speculative. We suggest that they are related to basin geometry and heterogenous temperature evolutions in regions from where thermocline waters are sourced. A positive feedback loop between source region temperature and tropical cyclone activity may have amplified tropical thermocline adjustments.

中文翻译：

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热带大西洋温跃层深度的上新世演化

摘要。据推测，全球温度趋势与热带温跃层深度密切相关，温跃层浅滩在上新世晚期北半球冰川作用加剧中发挥了关键作用。太平洋的上新世温跃层演化已有详细记录并支持这一假设，但热带大西洋的温跃层记录有限。我们在东赤道大西洋 (EEA) 的海洋钻探计划站点 959 提供了来自晚上新世间隔的新浮游有孔虫 Mg/Ca、δ ¹⁸ O 和 δ ¹³ C 记录，我们用它们来重建海洋温度和盐度和盐度的相对变化。温跃层深度。数据是使用表面居住的Globigerinoides ruber生成的和地下居住的Neogloboquadrina dutertrei。地表和地下记录之间的梯度降低表明，在中皮亚琴茨暖期结束时，EEA 温跃层加深（mPWP；~3.3-3.0 Ma）。我们将上新世晚期记录与先前发表的上新世早期 δ ^{18 联系起来}O 来自 Site 959 的数据并将其与加勒比海的 Site 1000 进行比较。在上新世的过程中，EEA 和加勒比海的温跃层变化遵循类似的模式，显着的逐步温跃层在 ~5.5 到 4.0 Ma 之间加深，逐渐形成浅滩至 mPWP，然后在 mPWP 结束时轻微加深. 热带大西洋的热带温跃层深度演化与太平洋不同，太平洋的特点是上新世逐渐形成全盆地浅滩。这些结果可能挑战热带温跃层深度与全球气候之间的假设联系。周期性发散的太平洋和大西洋温跃层运动背后的机制仍然是推测性的。我们认为它们与温跃层水来源地区的盆地几何形状和非均质温度演变有关。源区温度和热带气旋活动之间的正反馈回路可能放大了热带温跃层的调整。