We propose conducting a series of ocean reanalyses of the 20th Century (1890-2005) using SODA to study tropical Pacific decadal variablility, its influence on El Niño, and the atmospheric teleconnections that lead to decadal climate change across North America. The study will use the SODA ocean data assimilation framework in conjunction with the recently released atmospheric reanalysis of the 20th Century to generate a state estimate of the global oceans. In addition to the baseline run, we will conduct a series of “data thinning” experiments whereby we degrade the observations to replicate data coverage for various periods of time throughout the 20th Century to calculate error in the ocean state estimate. In addition to the ocean reanalyses, we will use results from the reanalyses to drive an atmospheric general circulation model to sudy the impact of improved SST information on the modeled climate of North America. For the atmospheric modeling component we plan to utilize the Community Atmosphere Model 3 (CAM3) developed and distributed by the National Center for Atmospheric Research (NCAR). We will force the T85 resolution (1.4 degree) version of this model with the SST anomaly from SODA as well as SST reconstructions (such as HadISST) and compare the results to the results from the NCAR multi-century control runs. These control runs have been extensively analyzed and provide an accepted atmosphere background state with which we can compare our suite of runs. We will verify the model results, both from SODA and from the atmosphere model with 100-year long records from sources such as âˆ©Ã¼Ã±18O from corals from the tropical Pacific, sea level records from coastal tide guages, and from observations such as global precipitation rates that are currently available. The proposed research contributes to the goals of the Climate Variability Program by expanding our understanding of decadal climate variability, by providing initial conditions for decadal prediction models, and by exploring the causes of North American climate change. The resulting reanalysis will be available on our web site (soda.tamu.edu) to other researchers interested in topics such as AMOC and rapid climate transitions during the 20th Century.