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

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.

Variations of Carbonyl Sulfide During the Dry/Wet Seasons Over the Amazon

“…During January–March (wet season), precipitation values are high (>250 mm month −1 ). High precipitation will bring more water to plants and increase photosynthetic activity of plants (e.g., Albright et al., 2022), removing more OCS from the atmosphere. As a result, OCS values are low during January–March wet season (Figure 4b).…”

“…The results are shown in Figure 1. During January–March (wet season), more precipitation is associated with more photosynthesis over the Amazon basin (e.g., Albright et al., 2022). Since OCS is absorbed by vegetation during photosynthesis, OCS concentrations are relatively low over the Amazon basin during January–March (wet season) (Figure 1a).…”

Impact of El Niño Southern Oscillation on CO2 and Solar‐Induced Fluorescence Over the Indo‐Pacific Region

“…Figure 2c illustrates a plot between the SIF and CO 2 , which suggests a weak anti‐correlation, −0.20 (20% significance level), between them. Such a weak and insignificant correlation implies that atmospheric CO 2 is not determined only by photosynthetic activity (SIF), instead, atmospheric CO 2 is modulated by different variables, such as transport and CO 2 surface emission from fire (Albright et al., 2022; Jiang et al., 2023).…”

Solar-induced fluorescence products show variable skill in constraining global patterns in biospheric CO2 fluxes

“…Several existing studies provide a possible road map for how to connect atmospheric CO 2 observations with vegetation indicators. For example, a handful of studies directly compare the seasonal cycles of SIF against satellite-based CO 2 observations across the Amazon (e.g., Parazoo et al, 2013;Albright et al, 2022); these studies report that the seasonality of SIF and atmospheric CO 2 are modestly anti-correlated, implying that GPP is driving the seasonality of NBE in this region (Parazoo et al, 2013). Additional studies use SIF to help interpret space-time patterns in NBE estimated using atmospheric CO 2 observations and inverse modeling (e.g., Liu et al, 2017Liu et al, , 2020Byrne et al, 2021).…”