ERC advanced grant to Sue Trumbore on terrestrial carbon cycling

Within Earth System research, key processes and organisms that regulate exchanges of energy, water and elements between ecosystems and their surroundings are analyzed using observations, experiments and complex models. However, current Earth System Model predictions of land carbon (C) storage extrapolated over the next century are highly uncertain. They predict increases in productivity and C storage due to CO2 fertilization over the next decades, with effects of climate warming on decomposition and vegetation turnover accelerating losses over the latter part of the century. Getting both of these feedbacks right relies critically on factors controlling C dynamics in vegetation and soils. The age of C in, and respired by terrestrial ecosystems typically depend on processes that are poorly understood.

The overall goal of Sue Trumbore’s newly granted ERC project “14Constraint” is to enhance the availability and use of radiocarbon data as constraints for process-based understanding of the age distribution of carbon in and respired by soils and ecosystems.

Carbon enters ecosystems by a single process, photosynthesis. It returns by a range of processes that depend on plant allocation and turnover, the efficiency and rate of litter decomposition and the mechanisms stabilizing C in soils. Thus the age distribution of respired CO2 and the age of C residing in plants, litter and soils are diagnostic properties of ecosystems that provide key constraints for testing carbon cycle models. Radiocarbon, especially the transit of ‘bomb’ 14C created in the 1960s, is a powerful tool for tracing C exchange on decadal to centennial timescales. 14Constraint will assemble a global database of existing radiocarbon data and demonstrate how they can constrain and test ecosystem carbon cycle models. The project will furthermore fill data gaps and add new data from sites in key biomes that have ancillary data sufficient to construct belowground C and 14C budgets. Overall, this project is urgently needed before atmospheric 14C levels decline to below 1950 levels as expected in the next decade.