The Johnson team departed Honolulu, HI today on a 1 month research cruise heading towards San Diego, CA to study the effects of climate change on open ocean ecosystems. The research cruise is the third in a series designed to map and characterize key microbial populations in the ocean as a function of temperature. We are also measuring other environmental variables such as pH, dissolved inorganic carbon, nutrients and many other variables than regulate these populations and that are predicted to be affected by climate. Our work is focusing on Prochlorococcus as the most abundance phytoplankton in the ocean and how it responds to changes in temperature (both natural variability and experimentally induced). Our team, which is composed of undergraduates, graduate students, a K-12 educator and a science journalist, is joined by long-term collaborators from the University of Tennessee Knoxville (Zinser and Wilhelm labs) as well as collaborators from U Washington, MBARI, and NOAA. This work is supported in part by grants from the US NSF.