Along with the mean sea level rise due to climate change, the sea level exhibits natural variations at a large number of different time scales. One of the most important is the one linked with the seasonal cycle. In the Northern Hemisphere winter, the sea level is as much as 20 cm below its summer values in some locations. It is customary to associate these variations with the seasonal cycle of the sea surface net heat flux which drives an upper-ocean thermal expansion creating a positive steric sea level anomaly. Here, using a novel framework based on steric sea level variance budget applied to observations and to the Estimating the Circulation and Climate of the Ocean state estimate, we demonstrate that the steric sea level seasonal cycle amplitude results from a balance between the seasonal sea surface net heat flux and the oceanic advective processes. Moreover, for up to 50% of the ocean surface, surface heat fluxes act to damp the seasonal steric sea level cycle amplitude, which is instead forced by oceanic advection processes. We also show that eddies play an important role in damping the steric sea level seasonal cycle. Our study contributes to a better understanding of the steric sea level mechanisms which is crucial to ensure accurate and reliable climate projections.

随着气候变化导致的平均海平面上升，海平面在许多不同的时间尺度上表现出自然变化。最重要的因素之一是与季节周期相关的因素。在北半球冬季，某些地区的海平面比夏季值低 20 厘米。通常将这些变化与海面净热通量的季节周期联系起来，海面净热通量驱动上层海洋热膨胀，从而产生正空间海平面异常。在这里，使用基于空间海平面方差预算的新颖框架应用于观测和海洋状态估计的环流和气候估计，我们证明空间海平面季节性循环幅度是由季节性海面净值之间的平衡产生的热通量和海洋平流过程。此外，对于高达 50% 的海洋表面，表面热通量会抑制季节性空间海平面循环幅度，而这种幅度是由海洋平流过程推动的。我们还表明，涡流在抑制空间海平面季节性循环方面发挥着重要作用。我们的研究有助于更好地了解海平面立体机制，这对于确保准确可靠的气候预测至关重要。