Beyond the Instrumental Record: The Case of Circulation at the Last Glacial Maximum

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OCE-0645936The modern ocean circulation state is being successfully estimated by combining a wide array of instrumental observations with an oceanic general circulation model. This state estimate is made possible through technical advances in numerical optimization methods and the development of new expertise within the community. This infrastructure will be applied toward determining the circulation of the Last Glacial Maximum (LGM). The LGM is very important for the overall understanding of climate change. In addition, it represents an earth differing radically from what we have today thus providing an opportunity to test and understand ocean models under very different boundary conditions. Considerable LGM data has been amassed over the last 20 years, to include nutrient, transient and dynamically active proxy data, and can be systematically used toward making a full oceanic state estimate, including the atmospheric forcing. Intellectual merit: Understanding contemporary and future climate change is only possible within the context of what has happened in the past from natural causes. The intention of this project is to use the modeling capabilities, physical insights, and optimization methodologies originally developed for the modern system to determine the ocean component of the climate of the LGM and the atmospheric conditions that brought it about. Secondarily, the ability to simulate the LGM would demonstrate that the models used to study modern and future climate states are not simply tuned to replicate modern observations, thus providing greater confidence in their results. Another by-product should be increased understanding of the specific information content of sometimes opaque proxy data. Broader impacts: The extent to which models of modern climate have true skill is difficult to quantify because they have undergone adjustments and tuning over many decades of development, and which may make them appear realistic for the wrong reasons. To the degree that the same model can quantitatively reproduce the ocean component of the climate system under very different forcing produces the same sort of confidence that one would gain by having a different earth-like planet to be used to test the models. The successful completion of this project will document the natural change in ocean circulation between the present and LGM. More generally, determining the range of past oceanic variability bears directly on the question of how much of contemporary climate change is forced by anthropogenic change and how much is natural. The work will be embedded in a wide-ranging academic program directed at understanding climate on nearly all time and space scales, and we expect interaction with students, post-docs and colleagues interested in most aspects of past, present, and future climate change.