Geologic intervals of sustained warmth such as the mid-Pliocene Warm Period can inform our understanding of future climate change, including the long-term consequences of oceanic uptake of anthropogenic carbon. Here we generate carbon isotope records and synthesize existing records to reconstruct the position of water masses and determine circulation patterns in the deep Pacific Ocean. We show that the mid-depth carbon isotope gradient in the North Pacific was reversed during the mid-Pliocene compared with today, which implies water flowed from north to south and deep water probably formed in the subarctic North Pacific Deep Water. An isotopically enabled climate model that simulates this North Pacific Deep Water reproduces a similar carbon isotope pattern. Modelled levels of dissolved inorganic carbon content in the North Pacific decrease slightly, although the amount of carbon stored in the ocean actually increases by 1.6% relative to modern due to an increase in dissolved inorganic carbon in the surface ocean. Although the modelled Pliocene ocean maintains a carbon budget similar to the present, the change in deep ocean circulation configuration causes pronounced downstream changes in biogeochemistry.

持续温暖的地质间隔，如上新世中期暖期，可以帮助我们了解未来的气候变化，包括海洋吸收人为碳的长期后果。在这里，我们生成碳同位素记录并综合现有记录以重建水团的位置并确定深太平洋的环流模式。我们表明，与今天相比，上新世中期北太平洋的中深度碳同位素梯度与今天相比发生了逆转，这意味着水从北向南流动，深水可能形成于亚北极北太平洋深水。模拟北太平洋深水的同位素启用气候模型再现了类似的碳同位素模式。北太平洋溶解无机碳含量的模拟水平略有下降，尽管由于表层海洋中溶解无机碳的增加，海洋中储存的碳量实际上比现代增加了 1.6%。尽管模拟的上新世海洋保持与现在相似的碳预算，但深海环流配置的变化导致下游生物地球化学发生显着变化。