The ocean is a major influence on weather and climate. With this set of lessons, middle school Earth systems science teachers can help their students build an understanding of how large bodies of water can serve as a heat source or sink at different times and how proximity to water moderates climate along the coast. The activity's combination of laboratory investigation, map study, and graphing applies different learning styles and provides practice in important science processes. The activities are adapted from "Earth Systems Education Activities for Great Lakes Schools: Great Lakes Climate and Water Movement" (V. J. Mayer et al. 1996). (Contains 6 figures and 4 resources.)