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Research Article: Long-term temporal variability of chlorophyll-a and sea surface temperature in the southern Caspian Sea using MODIS satellite observations (2002–2020)
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E. Hajiradkouchak *1   , H. Nasrollahzadeh Saravi2 , H. Fazli2 , B. Rahnama2 , M. Khoshnamvand2 |
1- Caspian Sea Ecology Research Center, Iranian Fisheries Science Research Institute (IFSRI), Agricultural Research, Education and Extension Organization (AREEO), Sari, Iran , eisa.hajirad@iau.ac.ir
2- Caspian Sea Ecology Research Center, Iranian Fisheries Science Research Institute (IFSRI), Agricultural Research, Education and Extension Organization (AREEO), Sari, Iran |
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Abstract: (24 Views) |
Sea surface temperature (SST) and chlorophyll-a (Chl-a) are important indicators of climatic variability and phytoplankton biomass. This study investigated temporal trends in SST and Chl-a and their relationship in the southern Caspian Sea at monthly and seasonal scales during 2002–2020. MODIS-Aqua and MODIS-Terra satellite data were used to construct long-term time series following standard image preprocessing, atmospheric correction, and retrieval using Multi‑Channel SST (MCSST) for SST and OC3M for Chl-a. Seasonal trends were assessed using the Mann–Kendall test, while the Pettitt’s test was applied to identify abrupt changes. Linear regression was used to examine the relationship between SST and Chl-a. Chl-a showed a significant increasing trend, with mean concentrations rising from 2.95 mg m⁻³ in 2002 to 4.52 mg m⁻³ in 2020. In contrast, mean SST increased slightly from 15.1°C to 16.1°C, but no significant monotonic trend was detected. The Pettitt’s test identified a significant change point in Chl-a around mid-2006. Regression analysis indicated a moderate positive relationship between SST and Chl-a, with SST explaining 57.5% of the observed variability (R²=0.575, p<0.05). The increasing Chl-a trend despite the absence of a significant SST trend suggests that factors beyond temperature, including nutrient inputs and river discharge, may contribute to phytoplankton variability. Overall, the findings highlight the value of long-term satellite observations for monitoring ecological changes in the southern Caspian Sea ecosystem.
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| Keywords: Caspian Sea, Chl-a, Sea surface temperature, Remote sensing, Time series analysis, Phytoplankton biomass |
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Full-Text [PDF 655 kb]
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Type of Study: Orginal research papers |
Subject:
Ecology
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