Seasonal Variations of Solar-Induced Fluorescence, Precipitation, and Carbon Dioxide Over the Amazon

Ronald Albright; Abigail Corbett; Xun Jiang; Ellen Creecy; Sally Newman; King-Fai Li; Mao-Chang Liang; Yuk L Yung

doi:10.1029/2021EA002078

Seasonal Variations of Solar-Induced Fluorescence, Precipitation, and Carbon Dioxide Over the Amazon

Earth Space Sci. 2022 Jan;9(1):e2021EA002078. doi: 10.1029/2021EA002078. Epub 2022 Jan 18.

Authors

Ronald Albright¹, Abigail Corbett^{1

2}, Xun Jiang¹, Ellen Creecy¹, Sally Newman³, King-Fai Li⁴, Mao-Chang Liang⁵, Yuk L Yung^{6

7}

Affiliations

¹ Department of Earth & Atmospheric Sciences University of Houston Houston TX USA.
² SeekOps Inc Austin TX USA.
³ Bay Area Air Quality Management District San Francisco CA USA.
⁴ Department of Environmental Sciences University of California Riverside CA USA.
⁵ Institute of Earth Sciences, Academia Sinica Taipei Taiwan.
⁶ Division of Geological and Planetary Sciences, California Institute of Technology Pasadena CA USA.
⁷ Jet Propulsion Laboratory Pasadena CA USA.

Abstract

Previous studies suggested that the Amazon, the largest rainforest on Earth, changes from a CO₂ sink to a CO₂ source during the dry/fire season. However, the biospheric contributions to atmospheric CO₂ are not well understood during the two main seasons, the dry/fire season and the wet season. In this article, we utilize Orbiting Carbon Observatory 2 (OCO-2) Solar-Induced Fluorescence (SIF) to explore photosynthetic activity during the different seasons. The spatiotemporal variability of OCO-2 SIF, OCO-2 CO₂, precipitation, and burned area are investigated over the Amazon from September 2014 to December 2019. Averaging over the entire Amazon region, we found a positive temporal correlation (0.94) between OCO-2 SIF and Global Precipitation Climatology Project precipitation and a negative temporal correlation (-0.64) between OCO-2 SIF and OCO-2 CO₂, consistent with the fact that precipitation enhances photosynthesis, which results in higher values for SIF and rate of removal of CO₂ from the atmosphere above the Amazon region. We also observed seasonality in the spatial variability of these variables within the Amazon region. During the dry/fire (August-October) season, low SIF values, low precipitation, high vapor pressure deficit (VPD), large burned areas, and high atmospheric CO₂ are mainly found over the southern Amazon region. In contrast, during the wet season (January-March), high SIF values, high precipitation, low VPD, smaller burned areas, and low CO₂ are found over both the central and southern Amazon regions. The seasonal difference in SIF suggests that photosynthetic activity is reduced during the dry/fire season relative to the wet season as a result of low precipitation and high VPD, especially over the southern Amazon region, which will contribute to more CO₂ in the atmosphere during the dry/fire season.

Keywords: Photosynthesis; biosphere‐atmosphere exchange; burned area; vapor pressure deficit.