Different Types of Surface Chlorophyll Patterns of Oceanic Mesoscale Eddies Identified by AI Framework

Abstract

Oceanic mesoscale eddies (with scale 10¹–10² km) and their submesoscale fine structures (with scale 10⁰–10¹ km) can effectively induce vertical motions and bring nutrients into the oceanic euphotic layer, which leaves abundant footprints on the ocean surface chlorophyll distributions and have the potential to promote primary productivity of oceanic ecosystem. In return, these surface chlorophyll footprints observed by ocean color satellites can serve as a useful tool to reveal the spatial structures of mesoscale eddies and their submesoscale fine structures. By combining artificial intelligence (AI) algorithms to develop a series of identification strategies for typical surface chlorophyll patterns around mesoscale eddies, we find that over 20% of mesoscale eddy observations exhibit identifiable typical chlorophyll patterns, which tends to regulate an increase of the surface chlorophyll concentration within the corresponding eddies, especially enhancing by about 30% in nutrient-restricted subtropical regions compared with the background values. Based on their geometric features, typical chlorophyll patterns are primarily classified as Core, Spiral, Tail, Ring, Loop, and Eye respectively by clustering algorithm. Further spatial-spectral analysis found that the typical patterns on eddies exhibit a much steeper wave-number spectral slope about −3, compared to the non-typical distributions on eddies and the non-eddy background distribution (about −2.7–−2.2). This implies that the occurrence of different typical chlorophyll patterns may correspond to specific mesoscale and submesoscale dynamic processes.