Interannual Variability of Summer Net Ecosystem CO 2 Exchange in High Arctic Tundra

• Published in: Journal of geophysical research. Biogeosciences 2021-08, Vol.126 (8)
• Main Authors: Braybrook, Christina A., Scott, Neal A., Treitz, Paul M., Humphreys, Elyn R.
• Format: Article
• Language: English
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2020JG006094

Arctic terrestrial ecosystems may be contributing to increasing atmospheric carbon dioxide (CO 2 ) concentrations under amplified climate change at high‐latitudes. This research investigates how summer net ecosystem CO 2 exchange (NEE) and its component fluxes, gross primary production (GPP), and ecosystem respiration (R eco ) varied over five years (2008, 2009, 2010, 2012, and 2014) at the Cape Bounty Arctic Watershed Observatory (74.92°N, 109.58°W). The eddy covariance technique was used to measure NEE and a combined light and temperature response model was used to partition NEE into GPP and R eco . Total summer NEE varied from −19.8  to 7.9 g C m −2 . Despite two summers with net CO 2 uptake, this tundra was likely a source of CO 2 on an annual basis. In most years, growing degree days with a base 0°C (GDD 0 ) had more predictive power than other environmental variables in random forest analyses of daily NEE. Interannual variability in total summer NEE over the five study years was also attributed to greater variability in GPP than R eco (coefficient of variation: 62% and 27%, respectively). However, total summer GDD 0 significantly correlated with total summer R eco but not NEE nor GPP. Instead, summer total NEE and GPP significantly correlated with satellite‐derived normalized difference vegetation index (NDVI), which may have exhibited carry‐over effects from one year to the next to limit the impact of current year GDD 0 on total summer NEE at this tundra site. Arctic ecosystems currently store a vast amount of carbon within frozen soils. Over the last two decades, Arctic surface air temperatures have increased at a rate twice the global average, which has the potential to shift terrestrial carbon cycling, ultimately impacting atmospheric carbon dioxide (CO 2 ), a potent greenhouse gas. Whether Arctic terrestrial ecosystems are releasing more CO 2 than they are absorbing is important, as this can impact the global climate system. This research measured CO 2 exchange between the atmosphere and the tundra over five summers at the Cape Bounty Arctic Watershed Observatory (74.92°N, 109.58°W) on Melville Island, Nunavut, Canada. The ecosystem acted as a CO 2 source for three out of five summers and is likely an annual net CO 2 source to the atmosphere. Interannual differences in weather appeared to impact plant productivity and CO 2 uptake more than decomposition and respiration and CO 2 emissions to the atmosphere at this site. The amount of CO 2 absorbe