In recent decades, oceans have taken up roughly 30% of the CO₂ emitted to the atmosphere by human activities. This capacity will diminish in the future though, as the oceans’ CO₂-buffering capacity is reduced and they become more acidic. Despite this expected decline, the sheer size of the ocean carbon reservoir means that oceans will remain the ultimate sink for much of our anthropogenic CO₂ over the next few centuries. Oceans not only play a key role in controlling atmospheric CO₂ content today, but also were critical factors in global carbon cycling throughout Earth’s history. This course will examine the ocean carbon cycle and its more important controlling processes, such as ocean circulation (physics), primary production and degradation of organic matter (biology), CO₂ acid-base reactions (chemistry), and continental weathering and marine sedimentation (geology). The course begins with an examination of ocean physics, including Ekman dynamics, western boundary current, gyre circulation, stratification, intermediate- and deep-water formation, and global thermohaline circulation. Observations of tracers, such as radiocarbon and CFCs whose distribution reflects ocean dynamics, will be used to complement the class’ theoretical discussion. We will then consider some aspects of marine biology, such as mechanisms of seasonal bloom, dependence of surface ocean production on nutrients and temperature, and the export of organic matter to the deep ocean. Satellite images and measurements of oxygen, phosphorus, and nitrogen will be used to illustrate these processes and elucidate the spatial and temporal patterns of primary production. The class will move on to an examination of CO₂ chemistry in seawater and air-sea gas exchange, including concepts of solubility and chemical and isotopic equilibrium concentrations. “Bomb” radiocarbon, produced by thermonuclear bomb testing in the 1950-1960s, will be used to constrain the global rate of air-sea gas exchange. To gain a geological perspective on global carbon cycle change, we also consider how long term processes, such as weathering of continental silicate rocks and carbonate sedimentation, help control atmospheric CO₂ levels. With this cumulative understanding, the course will conclude by addressing global issues, such as the fate of fossil fuel CO₂, glacial-interglacial atmospheric CO₂ variations, and CO₂-temperature negative feedback mechanisms that may have maintained liquid water over billions of years during which the energy output of the Sun has increased.

    Interdisciplinary in design, the course will strive for a quantitative description of ocean biogeochemistry, using observations whenever possible to illustrate basic processes and concepts. Participants are expected to attend class and complete assigned readings. Grading will be based on the final exam and biweekly homework assignments.