PNNL

Abstract

In boreal summer, daily gross primary productivity (GPP) of northern high latitude (NHL, 40°N to 90°N) is substantial, reaching ~80% of daily tropical GPP, but is highly uncertain (see Figure 11, Norton et al., 2019). Model benchmarking of NHL GPP is challenging because direct measurements of GPP on regional to pan-Arctic scales do not exist; however, carbonyl sulfide (OCS) provide an important proxy for photosynthetic carbon uptake. The aircraft vertical profiles provide regional scale sensitivity. In this study, we couple a OCS simulation with the GEOS-CHEM global transport model to fit aircraft profiles acquired over Alaska during NASA’s Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE 2012-2015) to optimized OCS fluxes across the NHL. We use the empirical biome-specific linear relationship between plant uptake of OCS and GPP to derive the GPP-based plant uptake and then simulate OCS. We evaluate the six simulations against CARVE optimized estimates and estimate an integrated NHL plant uptake of -247 Gg S year-1 in the NHL, which is about 25% higher than the ensemble mean derived from the six GPP models. GPP-derived fluxes systematically underestimate the peak growing season across the NHL, while a subset of models predict early start of season in Alaska, consistent with previous studies of net ecosystem exchange. Our results suggest that further work is needed to fully understand the environmental and biotic drivers and quantify their rate of photosynthetic carbon uptake in Arctic ecosystems. This frame work can be applied to a global scale.