Assessing the Spatio-Temporal Variability of Chlorophyll-A across Cabo Verde using Remote Sensing Data

Abstract

Chlorophyll-a (Chl-a) is used as a proxy to estimate the biomass of phytoplankton which, as the base of the marine food web, plays a crucial role in assessing the health and productivity of marine ecosystems. This study aims to evaluate the seasonal and interannual variability of Chl-a and investigate the parallel changes in SST as an indicator of some physical process in the ocean. By using satellite imagery from MODIS-Aqua, captured monthly at a 4 km resolution, the study provides insights into the spatio-temporal distribution of Chl-a and Sea Surface Temperature (SST). The results reveal distinct seasonal patterns, with maximum Chl-a occurring in January (around 0.32 mg/m³) and minimum values observed in August (approximately 0.15 mg/m³) in Cabo Verde as well as an inverse relationship between Chl-a and SST. These seasonal variabilities in Chl-a are accompanied by corresponding changes in SST, with peak temperatures occurring in September (around 27 °C) and low temperatures in January (approximately 23 °C). The analysis also identifies abnormal years, such as 2010, 2011, 2015, and 2018, characterised by deviations from the seasonal average Chl-a patterns. Additionally, a regime shift in Chl-a starting in 2013 is observed, with an overall increasing trend until 2022. Furthermore, the analysis demonstrates the relationship between Chl-a and SST variability in small pelagic fish and tuna respectively. These findings can help stakeholders for sustainable fishing and conservation in Cabo Verde. Further integration of environmental variables can enhance models predictive and the understanding of Chl-a dynamics in Cabo Verde.