Using Chlorophyll Fluorescence to Assess the Impact of Agriculture on Northern Hemisphere CO2 Seasonality

Abstract:

The seasonality of carbon dioxide (CO₂) concentrations in the northern hemisphere (NH) has increased by up to 50% over the previous five decades. A significant portion of this increase may be explained by enhanced agricultural productivity. The impact that increased crop production has on CO­­₂ seasonality is dependent on the fraction of the crop Gross Primary Product (GPP) that occurs during the natural carbon uptake period (CUP). Solar Induced Fluorescence (SIF), an artifact of photosynthesis, can be used to assess GPP directly via remote sensing. New methods for measuring SIF from space provide tools for obtaining GPP data at regional and global levels. We use SIF data from the GOSAT and OCO-2 satellites to obtain observational estimates of the fraction of GPP occurring within the CUP in NH agricultural regions. We compare these fractions with estimates made using crop calendars and inventories and, where available, with CO₂ flux data from eddy covariance towers. Our results offer insight into the impact that increased agricultural productivity has on the seasonal amplitude of NH CO₂ concentrations.