Keeling, Ralph: UCSD Scripps Institution of Oceanography (Project Lead)
Project Funding:
2014 - 2017
NRA: 2013 NASA: Carbon Cycle Science
Funded by DOE
Abstract:
exchanges of CO2 with the atmosphere on decadal and longer time scales. The approach involves carrying out time series measurements of CO2 concentration and isotopes and uses these and other datasets to challenge and improve carbon cycle models, including earth system models. The proposal particularly emphasizes the use of these data to improve understanding of changes occurring in boreal and Arctic ecosystems over the past 50 years and to seek from these data improved understanding of large-scale processes impacting carbon cycling, such as the responses to warming, CO2 fertilization, and disturbance. This proposal is responsive to the solicited research Theme #1, specifically relating to carbon cycling in Arctic and boreal regions. It is also responsive to the need for improved observations, solicited under “cross-cutting research activities”¯ by providing an archive of CO2 samples extracted from flasks that may promote the development of novel isotopic applications related to land carbon cycling (e.g. radiocarbon).
The proposal specifically seeks support for continuing measurements of CO2 concentrations and isotopes from the Scripps CO2 program from flasks collected at an array of ten stations distributed from the Arctic to the Antarctic. It also seeks support for modeling studies and interpretive work to expand on the recent discovery based on airborne data that the amplitude of the seasonal cycle is cycle has increased by 50 to 60% since 1960 at latitudes north of 40N. This amplitude increase stands out as perhaps the most compelling evidence to date for wide-spread changes in land carbon cycling relevant for the global CO2 balance and climate change. Understanding its causes and improving terrestrial ecosystem models to depict the relevant processes is therefore clearly a high priority. This proposal will focus on key questions: 1) How is the amplitude increase related to changes in net carbon flux in boreal and arctic systems? 2) What processes are responsible for the amplitude increase? 3) How can the models be improved to incorporate the relevant processes?
Work to address these questions will entail inverse modeling activities in collaboration with colleagues in Germany (MPI Jena) and Japan (JAMSTEC) to further assess the relationship between the changing atmospheric CO2 cycles and the net CO2 fluxes over the past 50 years. These simulations will use aircraft and surface data to provide improve estimates of the relationship between the seasonal cycles and the changing northern land sink over the past 50 years. The work will also entail carrying out factorial simulations using the CLM4.5 module of CESM to explore mechanistic links between changing the phasing and amplitude changes in atmospheric CO2 and its isotopes in relation to key parameters governing the arctic and boreal regions, assessing impacts of temperature sensitivity, CO2 sensitivity, light-use efficiencies, and water-use efficiency. Finally, we will expand upon the insights from CLM4.5 by also examining output from available runs from a large suite of land ecosystem models recently made available from the Trendy model comparison study, particularly assessing the impact of warming and CO2 fertilization and their interaction on CO2 amplitudes and phasing and in relation to net carbon sinks.
Publications:
Keeling, R. F., Graven, H. D., Welp, L. R., Resplandy, L., Bi, J., Piper, S. C., Sun, Y., Bollenbacher, A., Meijer, H. A. J. 2017. Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis. Proceedings of the National Academy of Sciences. 114(39), 10361-10366. DOI: 10.1073/pnas.1619240114
More details may be found in the following project profile(s):
