Effects of an eastward shift in the Agulhas retroflection region on chlorophyll-a bloom on its south flank

Abstract

As observed by remote sensing images in December 2013 and January 2014, chlorophyll-a (Chl-a) bloom occurred on the south side of the Agulhas Current (38°S-45°S). The dynamic mechanisms of Chl-a bloom were studied by satellite remote sensing data, reanalysis data and Argo data. The periodic shedding of the Agulhas ring led to a significant eastward shift of the Agulhas retroflection from December 2013 to January 2014, without the obstruction of flowing complex eddies and with increased current flow. Then, the horizontal transfer of Chl-a occurred along the south side of the Agulhas Current (38°S-45°S). Nitrate concentrations reached 10–15 μmol·L-1 on the south side of the Agulhas Current, where a deepened mixed layer and upwelling and the vertical transport of nutrients contributed to the Chl-a bloom. In addition, sufficient light and suitable precipitation provide good conditions for Chl-a bloom on the south side of the Agulhas Current.

Chlorophyll bloom triggered by tropical storm chedza at the southern tip of madagascar island

“…Adequate nutrients are an essential condition for phytoplankton blooms. Ding used the distribution of nitrate in the Agulhas Reflection Zone to investigate the mechanism of phytoplankton blooms (Ding et al 2023). Phytoplankton blooms in the southern part of the Indian Peninsula (Tan et al 2022), the southeastern Arabian Sea (Lu et al 2020),the Bay of Bengal (Xia et al 2022), and other seas have also been used to explore the mechanism of the bloom by using the nitrate distribution in the study area as an important indicator.…”