Yu Xiaolong, Barkan Roy, Naveira Garabato Alberto C
School of Marine Sciences, Sun Yat-sen University, and Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China.
Department of Geosciences, Tel Aviv University, Tel Aviv, Israel.
Nat Commun. 2024 Oct 25;15(1):9214. doi: 10.1038/s41467-024-53551-4.
Upper-ocean fronts are an important component of the global climate system, regulating both the oceanic energy cycle and material transports. In the common paradigm, upper-ocean fronts are generated by frontogenesis at the mesoscale (20-300 km), driven predominantly by confluent horizontal flows initiated by a background straining field. However, the mechanisms by which this frontogenesis extends down to and influences the submesoscale (0.2-20 km), which dominates vertical transports in the ocean, are still understudied. Here, we provide direct observational evidence that submesoscale frontogenesis, defined as the rate at which submesoscale buoyancy gradients intensify, is closely linked to convergent flows. Analysis of year-long measurements by a mooring array in the North Atlantic indicates that both the upper-ocean frontogenetic rate and the horizontal convergence exhibit strong seasonality and scale dependence, with larger magnitudes in winter and at smaller horizontal scales (down to at least 2 km). The frontogenetic rate is found to correlate more strongly with horizontal convergence as the scale decreases, suggesting that convergent flows are the main driver of submesoscale frontogenesis. Crucially, a rapid forward cascade of kinetic energy and enhanced vertical velocities preferentially occur during periods of submesoscale frontogenesis. Our findings highlight a mechanism underpinning the key role of submesoscale fronts in the oceanic kinetic energy cascade and as a focus of vertical transports, and call for a parameterization of such effects in climate-scale ocean models.
海洋上层锋面是全球气候系统的重要组成部分，它调节着海洋能量循环和物质输送。在通常的范式中，海洋上层锋面是由中尺度（20 - 300千米）的锋生作用产生的，主要由背景应变场引发的汇合水平流驱动。然而，这种锋生作用向下延伸并影响海洋中主导垂直输送的亚中尺度（0.2 - 20千米）的机制仍未得到充分研究。在此，我们提供了直接的观测证据，表明亚中尺度锋生作用（定义为亚中尺度浮力梯度增强的速率）与汇合流密切相关。对北大西洋一个系泊阵列长达一年的测量分析表明，海洋上层锋生速率和水平汇合都表现出强烈的季节性和尺度依赖性，冬季和较小水平尺度（至少低至2千米）时幅度更大。研究发现，随着尺度减小，锋生速率与水平汇合的相关性更强，这表明汇合流是亚中尺度锋生作用的主要驱动力。至关重要的是，在亚中尺度锋生作用期间，动能会快速向前级串，垂直速度也会增强。我们的研究结果突出了一种机制，该机制支撑着亚中尺度锋面在海洋动能级串中的关键作用以及作为垂直输送的焦点，并呼吁在气候尺度的海洋模型中对这种效应进行参数化处理。
