The modern Indo-Pacific oceans absorb more heat from the atmosphere than they release. The resulting energy surplus is exported from the Indo-Pacific by the ocean circulation and lost to the atmosphere from other ocean basins. This heat transport ultimately sustains much of the buoyancy lost to deep water formation at high latitudes, a key component of the global overturning circulation. Despite the fundamental link between inter-basin ocean heat transport and global overturning in today's climate, there is no general understanding of how these phenomena vary with climate state. Here, we use an unprecedented suite of fully-coupled climate model simulations, equilibrated for thousands of years to a wide range of CO₂ levels, to demonstrate that major differences in overturning between climates are related to systematic shifts in ocean heat transport between basins. Uniformly, equilibration to higher CO₂ levels strengthens inter-basin ocean heat transport and global deep water formation. These changes are sustained by increased surface heat uptake within the Indo-Pacific oceans, and increased high-latitude heat loss outside of the Indo-Pacific oceans as the climate warms. However, poleward heat transport and high-latitude heat loss do not increase symmetrically between hemispheres. Between glacial and modern-like states, North Atlantic heat loss intensifies and overturning in the Atlantic strengthens. In contrast, between modern-like and hot climates, heat loss and overturning strengthens in the Southern Ocean. We propose that these differences are linked to a shift in the relative efficiency of northward and southward ocean heat transport — dominated by advection in the North Atlantic and eddy diffusion in the Southern Ocean — with climate state. Our results suggest that, under high CO₂, future ocean heat transport towards Antarctica would increase disproportionately compared to its changes since the last ice age.

现代印度洋-太平洋海洋从大气中吸收的热量多于释放的热量。由此产生的能量过剩通过海洋环流从印度洋-太平洋输出，并从其他海洋盆地流失到大气中。这种热量传输最终维持了高纬度深水形成时失去的大部分浮力，这是全球翻转环流的关键组成部分。尽管在当今气候中跨流域海洋热传输与全球翻转之间存在基本联系，但对这些现象如何随气候状态变化尚无普遍了解。在这里，我们使用了一套前所未有的全耦合气候模型模拟，在数千年的时间里与各种 CO ₂水平，以证明气候之间翻转的主要差异与盆地之间海洋热量传输的系统转移有关。均匀地，平衡到更高的 CO ₂水平加强了流域间海洋热传输和全球深水形成。随着气候变暖，印度-太平洋海洋表面热量吸收增加，以及印度-太平洋海洋以外高纬度热损失增加，这些变化得以维持。然而，向极热传输和高纬度热损失不会在半球之间对称增加。在冰川国家和现代国家之间，北大西洋热损失加剧，大西洋倾覆加强。相比之下，在类似现代气候和炎热气候之间，南大洋的热量损失和倾覆加强。我们认为，这些差异与向北和向南海洋热传输的相对效率的变化有关 - 主要是北大西洋的平流和南大洋的涡流扩散 - 与气候状态有关。₂，与上次冰河时代以来的变化相比，未来向南极洲的海洋热量传输将不成比例地增加。