The ocean is changing vigorously on a wide range of time and space scales. This variability leads to substantial problems in observing and modeling (simulating) the rapidly changing flow field, the ocean’s temperature distribution, and more generally the consequences of those changes on a wide variety of scientific, military, and societal problems, including climate research, fisheries management, coastal pollution (spill) predictions, or ship routing. As an example, the ocean carries roughly 50% of the heat from the low latitudes to mid and high latitudes, where it is released to the atmosphere and moderates our climate. Any significant variation in this heat transport will necessarily lead to a perturbation of the climate system. Among the goals of the present ocean research are therefore to measure, understand, and eventually predict these variations by combining ocean data and ocean models.