Oceanic cross-density (diapycnal) mixing helps sustain the ocean density stratification and its Meridional Overturning Circulation (MOC) and is key to global tracer distributions. The Southern Ocean (SO) is a key region where different overturning cells connect, allowing nutrient and carbon rich Indian and Pacific deep waters, and oxygen rich Atlantic deep waters to resurface. The SO is also rife with intense diapycnal mixing due to the interaction of energetic eddies and currents with rough topography. SO diapycnal mixing is believed to be of secondary importance for the MOC. Here we show that changes to SO mixing can cause significant alterations to biogeochemical tracer distributions over short and long time scales in an idealized model of the AMOC (Atlantic MOC). While such alterations are dominated by the direct impact of changes in diapycnal mixing on tracer fluxes on annual to decadal time scales, on centennial time scales they are dominated by the mixing-induced variations in the advective transport of the tracers by the AMOC. This work suggests that an accurate representation of spatio-temporally variable local and non-local mixing processes in the SO is essential for climate models’ ability to (i) simulate the global biogeochemical cycles and air sea carbon fluxes on decadal time scales, (ii) represent the indirect impact of mixing-induced changes to AMOC on biogeochemical cycles on longer time scales.

海洋交叉密度（diapycnal）混合有助于维持海洋密度分层及其经向翻转环流（MOC），并且是全球示踪剂分布的关键。南大洋 (SO) 是一个关键区域，不同的倾覆细胞连接在一起，使富含营养和碳的印度和太平洋深水以及富含氧气的大西洋深水重新浮出水面。由于高能涡流和水流与崎岖地形的相互作用，SO 也充满了强烈的透孔混合。SO diapycnal 混合被认为对 MOC 来说是次要的。在这里，我们表明在 AMOC（大西洋 MOC）的理想化模型中，SO 混合的变化会导致生物地球化学示踪剂分布在短期和长期尺度上发生显着变化。虽然这种变化主要是在年度到十年时间尺度上，透孔混合变化对示踪剂通量的直接影响，但在百年时间尺度上，它们主要是混合引起的 AMOC 示踪剂平流传输的变化。这项工作表明，准确表示 SO 中时空可变的局部和非局部混合过程对于气候模型能够 (i) 在十年时间尺度上模拟全球生物地球化学循环和海气碳通量，(ii ) 表示混合引起的 AMOC 变化对较长时间尺度的生物地球化学循环的间接影响。