Collaborative Research Assessing the Simulated Simulated Arctic Freshwater System in CMIP5 Models, the CESM Large Ensemble, and Forced Simulations

Lead PI: Dr. Bruno Tremblay

Unit Affiliation: Ocean and Climate Physics, Lamont-Doherty Earth Observatory (LDEO)

August 2015 - July 2018
Project Type: Research

DESCRIPTION: The Arctic freshwater (FW) system is likely to undergo considerable change in coming decades with downstream impacts on ocean circulation, climate, and ecosystems. An ability to understand and project these impacts, in turn, will have important socio-economic influences on fisheries, energy distribution, and reinsurance industries, amongst others. However, the reliability of climate projections is uncertain and there is only a limited understanding of the importance of natural variability in the midst of anthropogenically forced change. This project seeks to address these issues through a series of modeling experiments and comparison of the model results with observational and reanalysis data sets. This project will contribute to STEM workforce development through provision of support to a young, early-career, female PI during the formative years of her career and support for the training of a graduate student. The PI will leverage her connections with the National Center for Atmospheric Research to include project results in their outreach exhibits for the general public. Results will also be included in public talks and university lectures. This project will investigate the following major science questions: 1. Do climate models show a consistent picture of projected Arctic Ocean FW changes during the 21st century and beyond? Are there obvious reasons for the model differences (e.g., resolution, sea ice model complexity, number of straits through the Canadian Arctic Archipelago, etc.)?   2. How large is the role of internal variability for different terms of the Arctic FW budget in climate simulations? How does this affect uncertainty in future projections at various timescales? How large does an ensemble need to be in order to capture the magnitude of internal variability?  3. How well do simulated FW components in Fram Strait and the switchyard region agree with observations from the last decade? What are the dynamics that lead to changes in FW from different sources?  To address these questions, first the Arctic Ocean freshwater (FW) budget in the suite of the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations for the 20th and 21st century will be assessed, followed by an analysis of the role of internal variability of terms of the Arctic FW budget in a large ensemble of simulations from the Community Earth System Model (CESM). Finally, the contribution of FW from different sources in Fram Strait and the Arctic switchyard region in the CESM will be compared with observations using new simulated FW tracers, and the Arctic Ocean dynamics leading to the variability of FW from different sources will be investigated. The Arctic Ocean FW budget has not been analyzed for the new generation of climate models participating in CMIP5, despite the changes that can be expected compared to CMIP3 due to the improvements to the simulation of the Arctic sea ice and the additional open passages in the Canadian Arctic Archipelago. The use of the large CESM ensemble provides an unique opportunity to assess the role of internal variability in terms of the Arctic FW budget, and comparisons to across-model scatter from CMIP5 will allow insight on the sources of uncertainty in future projections. Furthermore, the use of FW tracers in the CESM will allow a more detailed comparison with a new set of observations and will enable analysis of the dynamics that lead to the observed interannual variability of FW from different sources in two key regions in the Arctic.