Models project that with current CO₂ emission rates, the Southern Ocean surface will be undersaturated with respect to aragonite by the end of this century^1,2,3,4. This will result in widespread impacts on biogeochemistry and ocean ecosystems^5,6,7, particularly the health of aragonitic organisms, such as pteropods⁷, which can dominate polar surface water communities⁶. Here, we quantify the depth of the present-day Southern Ocean aragonite saturation horizon using hydrographic and ocean carbon chemistry observations, and use a large ensemble of simulations from the Community Earth System Model (CESM)^8,9 to track its evolution. A new, shallow aragonite saturation horizon emerges in many Southern Ocean locations between now and the end of the century. While all ensemble members capture the emergence, internal climate variability may affect the year of emergence; thus, its detection may have been overlooked by ensemble average analysis in the past. The emergence of the new horizon is driven by the slow accumulation of anthropogenic CO₂ in the Southern Ocean thermocline, where the carbonate ion concentration exhibits a local minimum and approaches undersaturation. The new horizon is also apparent under an emission-stabilizing scenario indicating an inevitable, sudden decrease in the volume of suitable habitat for aragonitic organisms.

模型预测，以当前的CO ₂排放速率，到本世纪末^1,2,3,4，相对于文石，南洋表面将不饱和。这将对生物地球化学和海洋生态系统^5,6,7产生广泛影响，尤其是对芦荟类生物⁷等农杆菌类生物的健康产生影响，它们可以在极地表水群落^6中占主导地位。在这里，我们使用水文学和海洋碳化学观测来量化当今南大洋文石饱和层的深度，并使用来自社区地球系统模型（CESM）^8,9的大量模拟跟踪其演变。从现在到本世纪末，南洋许多地方出现了一个新的浅文石饱和层。尽管所有合奏成员都捕捉到了出现，但内部气候的变化可能会影响出现的年份。因此，过去的整体平均分析可能忽略了它的检测。新视野的出现是由人为CO ₂在南洋大温跃层中缓慢积累驱动的，那里的碳酸盐离子浓度表现出局部最小值并接近饱和度。在稳定排放的情况下，新的视野也很明显，这表明不可避免地突然减少了适用于芦荟生物的适宜生境的数量。