Divergence Observation in a Mesoscale Eddy during Chla Bloom Revealed in Submesoscale Satellite Currents

Abstract

Oceanic mesoscale eddies continuously regulate the horizontal and vertical transport of mass, heat, salt, carbon, and nutrients throughout the ocean system owing to their ubiquity, three-dimensionality, and long-term persistence. Although satellites have been the main platforms used to observe mesoscale eddies and chlorophyll-a (Chla) distributions, they cannot support submesoscale physical–biological interactions. Contemporary satellite observations of Eulerian velocity fields are unable to resolve submesoscale processes that govern vertical migration and mixing, which are crucial for controlling the nutrients and light for phytoplankton in the surface layer. We explored the physical–biological interaction between the anticyclonic mesoscale eddy and the Chla secondary bloom that occurred after the spring bloom in the East/Japan Sea using the Geostationary Ocean Color Imager (GOCI). The GOCI currents were generated using GOCI Chla data and were used to map streamlines, vorticity, and divergence to characterize the surface current near the eddy. In the early spring bloom period, the eddy interior showed Chla depletion as the eddy was trapped externally. We found that the second bloom period coincided with a higher divergence or upwelling period in the eddy core, and a sharp Chla peak was observed when wind-induced Ekman suction was pronounced. This study describes the first satellite observation of surface layer divergence inside an anticyclonic mesoscale eddy with internal Chla blooms, utilizing a submesoscale-permitting GOCI-based surface current.

Using Landsat Image Series to Identify and Characterize Persistent Oceanographic Structures in a Dynamic Marine Protected Area (North of San Jorge Gulf, Argentinian Patagonia)

“…[12,[78][79][80]. Ocean color sensors, due to their many bands and the fact that they have been specifically designed for studies in the sea, allow the detection of mesoscale and even larger scale oceanographic processes (of the order of 100 km) [24,81] or even at submesoscale levels by applying models derived from vector geometry [82]. However, due to their low spatial resolution (several hundred meters), they are not appropriate for studies of coastal waters where submesoscale structures are of horizontal scales in the order of 1-10 km and time scales in the order of 1 day [26,83].…”

“…However, although in some cases some information about the presence of oceanographic fronts can be inferred from roughness differences, in general SAR images do not provide information about substances vertically transported by those fronts, such as chlorophyll, dissolved organic matter, etc., which in coastal sub-mesoscale processes affect biological productivity near the surface, and are easily detectable in the visible spectrum [24,36,83].…”

“…High-resolution satellite imagery provides a possibility to observe dynamical processes, such as the generation of eddies, mushroom-like current structures, filaments, etc. [23], that reveals the hidden physical dynamics that play an important role in the physical-biological interaction [24]. Since the 1970s, structures such as island wakes and headland eddies in coastal waters were identified from spaceborne and airborne remotely sensed imagery in the visible wavelengths with a spatial resolution of 80 m [25] or through a combination of aerial photography and enhanced terrestrial imagery [4].…”

A Systematic Review of the Application of GOCI to Water Quality Monitoring of Inland and Coastal Waters

“…Various studies have explored alternative models and algorithms for Chla estimation in ICWs. [94] explored the physical-biological interaction between anticyclonic mesoscale eddies and Chla secondary blooms after spring blooms in the East Sea and Japan Sea using the GOCI OC3G Chla products. [132] found diurnal changes in GOCI-derived Chla, with generally higher values in the afternoon than in the morning, and identified heterogeneities in the temporal and spatial domains.…”

A Systematic Review of the Application of the Geostationary Ocean Color Imager to the Water Quality Monitoring of Inland and Coastal Waters

“…ICWs, due to their high population density, are prone to ABs when certain meteorological conditions arise [86][87][88][89][90][91][92][93]. The impact of ABs, such as the reduction in dissolved oxygen and the release of toxins, presents major challenges to aquatic ecosystem management [9,[94][95][96]. Monitoring ABs is essential for improving water quality and the inhabitants' quality of life and reducing unnecessary losses.…”