The boreal forest has been described as one of the lungs of the earth due to its ability to take up tremendous amounts of atmospheric carbon dioxide seasonally during the summer and respire carbon…

This is a grant awarded by the National Aeronautics and Space Administration (NASA) to the University of Alaska Fairbanks (UAF) to study carbon exchange dynamics in the circum-Arctic boreal forest using observations from the Orbiting Carbon Observatory-2 (OCO-2) satellite. The $223,226 grant will fund efforts to measure the seasonality of atmospheric carbon dioxide (CO2) in the boreal forest, investigate inter-annual variability, and validate the high-latitude OCO-2 retrievals through ground-based observations. This work is complementary to NASA's Arctic-Boreal Vulnerability Experiment (ABoVE) and will provide valuable data for improving global estimates of carbon exchange, supporting planned missions like Sentinel-5P, GOSAT-2, CarbonSat, and ASCENDS. The grant will also support training of a graduate student. There is no set-aside designation for this award.

The boreal forest has been described as one of the lungs of the earth due to its ability to take up tremendous amounts of atmospheric carbon dioxide seasonally during the summer and respire carbon dioxide back into the atmosphere during winter. The imprint of seasonal carbon uptake by the boreal forest is seen throughout the northern hemisphere. The boreal forest lies in sub-arctic and arctic regions, which have been warming faster than global average warming, causing concern about how the region's ability to draw carbon dioxide out of the atmosphere is responding to changing climatic conditions. The boreal forest is a diverse set of ecosystems with the north-american and european boreal forests dominated by needle-leaf forest while the the asian boreal forest is dominated by deciduous needle-leaf forest (called larch or tamarack). These differences in vegetation type as well as differences in temperature, precipitation, soil moisture, and fire regime may give rise to different carbon exchange dynamics around the boreal forest. Therefore, IT is crucial that we study carbon exchange dynamics and their dependence on climate in the circum-arctic boreal forest. The orbiting carbon observatory-2 (OCO-2) measures column-averaged dry-air CO2 mixing ratio (XCO2) globally as well as probing vegetation state through solar induced fluorescence (SIF) observations. In this project, we propose using OCO-2 observations to measure the seasonality (seasonal amplitude and timing of drawdown) of atmospheric CO2 spatially around the boreal forest. Using multi-year data, we investigate the inter-annual variability of carbon dioxide seasonality on spatial region (forest type), vegetation photosynthetic state (SIF), as well as climate anomalies (e.g. temperature, precipitation, soil moisture, etc.). A challenge of using OCO-2 data to study boreal forest carbon exchange dynamics is that high-latitude retrieval geometries have higher airmass and thus present greater measurement challenges, which leads to very low throughput of successful XCO2 measurements as compared to lower latitudes. On the other hand, the amplitude of the XCO2 seasonal cycle is largest (>10 PPM) in the boreal forest region and convergence of polar-orbiting ground tracks gives increased density of sounding attempts. Validation of XCO2 in the boreal forest is also lacking due to having only a few ground-based column measurement sites near the forest. To address this lack of ground truth, we have been observing XCO2 using mobile EM27/sun spectrometers within the north-american boreal forest at fairbanks, AK for over a year and propose to continue these observations. We intend to study agreement between our observations and OCO-2 observations to improve confidence in high-latitude retrievals. We will study quality-assurance flags to increase OCO-2 throughput in the boreal forest. We propose collaboration with scientists from stations near and within the boreal forest in this validation / throughput increase effort. The result of these efforts will be improved density of validated observations in the boreal forest, enabling study of the key science questions above with global OCO-2 data. Our study is complementary the NASA arctic-boreal vulnerability experiment (above), which focuses on the north-american boreal forest. Determining if carbon dynamics are different in other parts of the boreal forest is critically important for extrapolation of above results to the rest of the boreal forest. Our observations also provide ground truth for atmospheric CO2, CH4, CO, and H2O that are crucial for improving global estimates of carbon exchange and will be valuable for planned missions such as sentinel-5P, gosat-2, carbonsat, and ascends. The project will also train a graduate student and results will be presented to the community through peer-reviewed publications and presentations at international scientific meetings.