Carbon Reservoirs on Earth

Oceanic Dissolved Organic Carbon

Oceanic dissolved organic carbon (DOC) represents one of the largest dynamic reservoirs of reduced carbon on Earth. At ~1018 g carbon, the DOC reservoir is of the same magnitude as all living vegetation on the Earth’s continents, and larger than the atmospheric CO2 pool. Many familiar compounds make up oceanic DOC, such as sugars, carbohydrates, amino acids, and lipids. Yet, few DOC measurements have been made of hydrothermal vent waters.

Measuring DOC

The MQ-1001 Dissolved Organic Carbon (DOC) Analyzer measures the concentration of DOC in any given sample. It works by injecting a very small amount of a water sample (100 mL) into a 750°C column. Because of the heat, any organic carbon in the sample is converted into CO2. We use an infrared detector to measure the amount of CO2 created from the injection. That tells us how much DOC was in the sample. Because seawater has much more inorganic carbon in it than organic carbon, we remove the inorganic carbon by acidifying the sample and purging it with O2 before we inject it into the DOC analyzer.