Scott Doney continues MIT's Marine Chemistry course (12.742, Fall 2006) with the second session on primary production. He works through the controls on phytoplankton growth, covering how light availability, nutrient supply, and temperature interact to set the pace of ocean photosynthesis. The lecture then shifts to the practical side of the subject, walking through the methods oceanographers use to actually measure primary production in the field, from tracking uptake rates to the assumptions built into common sampling techniques. Doney keeps the focus on the mechanics of measurement and the biological constraints researchers have to account for when interpreting data. Recorded as part of a full MIT OpenCourseWare series, the session runs 78 minutes and assumes some prior grounding in the course's earlier material on chemical oceanography.