remote sensing Article OCO-2 Solar-Induced Chlorophyll Fluorescence Variability across Ecoregions of the Amazon Basin and the Extreme Drought Effects of El Niño (2015–2016) Antony Oswaldo Castro 1,* , Jia Chen 2 , Christian S. Zang 1 , Ankit Shekhar 2,3 , Juan Carlos Jimenez 4 , Shrutilipi Bhattacharjee 2, Mengistie Kindu 1 , Victor Hugo Morales 5 and Anja Rammig 1 1 Technical University of Munich, TUM School of Life Sciences Weihenstephan, 85354 Freising, Germany;
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[email protected] Received: 14 January 2020; Accepted: 4 April 2020; Published: 8 April 2020 Abstract: Amazonian ecosystems are major biodiversity hotspots and carbon sinks that may lose species to extinction and become carbon sources due to extreme dry or warm conditions. We investigated the seasonal patterns of high-resolution solar-induced chlorophyll fluorescence (SIF) measured by the satellite Orbiting Carbon Observatory-2 (OCO-2) across the Amazonian ecoregions to assess the area´s phenology and extreme drought vulnerability. SIF is an indicator of the photosynthetic activity of chlorophyll molecules and is assumed to be directly related to gross primary production (GPP).