Submesoscale variability of subsurface chlorophyll-a across eddy-driven fronts by glider observations

英文摘要：Reflecting the local dynamic state of the pelagic system, subsurface chlorophyll maxima (SCM) are ubiquitous in the global ocean. Here, a high-resolution glider survey was conducted in the South China Sea to study the physical and biogeochemical change across the periphery of a mesoscale cyclonic eddy. We found intense vertical dispersion of SCM associated with enhanced diapycnal mixing at the frontal zones on the edge of the eddy. Submesoscale processes were found to play important roles within the eddy-driven fronts despite the general impact of the mesoscale Ekman upwelling and downwelling. Our results also suggested that wind-driven overturns at the frontal zone could result in a stronger gravitational instability at the northern edge of the eddy leading to an enhanced vertical mixing of subsurface Chl-a. However, turbulent mixing induced by symmetric instability with energy extracted from the lateral buoyancy gradient at the northeastern edge of the eddy had caused a divergence of the subsurface chlorophyll-a at the frontal zone. Our results provide direct evidence of the interaction between mesoscale and submesoscale processes at the oceanic frontal zone. These findings also call for tight cooperation between multidisciplinary observational and modeling approaches for a better understanding of the SCM variability and associated biogeochemical transformations at transient oceanic fronts

基于水下滑翔机观测的次表层叶绿素跨涡生锋面次中尺度变化

中文摘要：次表层叶绿素最大值（SCM）反映了水层的局部动力过程，在全球海洋中广泛分布。在此，本文基于南海的一次高分辨率水下滑翔机观测，研究了中尺度气旋涡旋边缘处，物理和生物跨锋面变化。本文发现伴随着涡旋边缘锋面区域跨等密面混合的增强，SCM的垂向耗散强烈，尽管受到中尺度Ekman上涌和下沉的影响，但涡生锋面的次中尺度过程仍起重要作用。研究结果表明，锋面区的翻转可能产生强重力不稳定使涡旋北部边缘的次表层叶绿素a垂向混合增强。然而，能量来自涡旋东北边缘的横向浮力梯度的对称不稳定进一步产生湍流混合，使次表层叶绿素a辐散。本文结果提供了中尺度和次中尺度过程相互作用的直接证据，有利于多学科观测和模拟方法的结合，以更好地理解海洋锋面处SCM变化和伴随的生化转换。