Potential carbon sources and sinks in frontal zones dominated respectively by mesoscale and submesoscale processes in the Luzon Strait

Abstract

The Luzon Strait experiences active ocean fronts resulting from the intrusion of the Kuroshio water, accompanied by substantial mesoscale and submesoscale processes. These processes induce variable patterns of upwelling and downwelling where submesoscale dynamics are often more intense than their mesoscale counterparts, profoundly affecting phytoplankton production and sedimentation. However, the ultimate role of these processes in the production and export of carbon remains unclear. We analyzed daily satellite and reanalysis data from 1999 to 2019, revealing the climatological patterns and spatial variations of mesoscale and submesoscale processes during both summer and winter, thereby identifying distinct frontal zones dominated by either mesoscale or submesoscale processes. Our results show that the cyclonic front area on the eastern side of the strait and anticyclonic front area along the Kuroshio axis, are significantly influenced by submesoscale processes. These areas are identified as potential carbon sinks due to enhanced nutrient availability and elevated sedimentation rates. Conversely, although mesoscale fronts contribute more significantly to Chlorophyll-a, the cyclonic front area on the western side of the strait, dominated by mesoscale processes, serves as a potential carbon source. This difference is attributed to the slower sedimentation rate of organic matter in the mesoscale region, which prolongs the decomposition of both in-situ and horizontally transported matter. These findings deepen our understanding of the impacts of mesoscale and submesoscale processes within frontal zones on the global carbon cycle.