Monitoring and estimating coastal upwelling using Sentinel-3 satellite imagery (case study: The Caspian Sea)

• Published in: Continental shelf research 2023-05, Vol.261, p.105010, Article 105010
• Main Authors: Ghorbani Afzal, Faezeh, Hasanlou, Mahdi, Rajabi-Kiasari, Saeed
• Format: Article
• Language: English
• Subjects: Caspian sea; Chl-a; Coastal upwelling; Fuzzy C-Means clustering; Remote sensing; Sentinel-3; SST
• ISSN: 0278-4343; 1873-6955
• DOI: 10.1016/j.csr.2023.105010

Delineation of upwelled zones is critical for the economy and physical processes of the coastal areas. The upwelling process is accompanied by vertical water motion, resulting in a surface with lower water temperature and increased chlorophyll-a contents (Chl-a). Since such patterns can be monitored using remote sensing technologies, this research investigates the potential of newly launched Sentinel-3 satellite imagery to gather information about the causes of summer upwelling in the Caspian Sea in 2017 and 2021. The upwelling spatial extent was determined using a Fuzzy C-means Clustering (FCM) approach. The UIwind index was also calculated to identify Ekman transport's involvement as an upwelling triggering factor. The results showed that during summer, the middle and south Caspian Sea had three upwelling cells, one in the eastern (cell 1) and two in the western regions (cells 2 and 3). FCM analysis revealed up to a 10 °C decline in SST, a 5 mg/m3 increase in Chl-a, and 70 km width during the upwelling events. •We assessed the causes of summer upwelling in the Caspian Sea using Sentinel-3 SLSTR and OLCI.•Coastal Upwelling can occur in both the western and eastern Caspian Sea (C1–C3).•Synoptic upwelling in C1 is mainly wind-induced (UIwind > 0.35 m2/s), followed by bottom topography and anti-cyclonic eddies.•While C3 upwelling is wind-driven, C2 can also be influenced by bottom topography and cyclones (August–September).•Cluster analysis revealed up to a 10 °C decline in SST, a 5 mg/m3 increase in Chl-a, and a 70 km width.