Inorganic Precipitation of Carbon in Productivity Experiments Utilizing Carbon-14

In a series of experiments where iron was added to natural waters and photosynthesis was measured by the radiocarbon method, we found that inorganic precipitation of carbon-14, presumably by mechanisms of occlusive coprecipitation, resulted from additions of 100 or more micrograms of iron per liter. Low levels of iron and prefiltered controls are suggested as correction measures.