NOAA Oceanic & Atmospheric Research | Climate Portal | Climate Program Office | Climate Observation Division

Why We Observe the Ocean

Ocean Carbon Uptake

• Measuring uptake of atmospheric carbon dioxide (CO2) by the ocean is necessary to better understand both the extent to which the ocean sequesters CO2 and how cycling among carbon reservoirs varies on seasonal-to-decadal time scales.

• Ocean-atmosphere exchange of CO2 by diffusion across the ocean surface results in ocean uptake of about a quarter of all anthropogenic CO2 emissions. As such, the ocean constitutes one of the largest sinks for the greenhouse gas most responsible for global climate change.

• Air-sea exchange of CO2 is a sensitive function of temperature, wind speed, sea surface roughness, ocean vertical mixing, precipitation, and local biological activity in the ocean. As a consequence, ocean uptake of CO2 varies greatly with season and location; indeed, some regions of the ocean are net sources while others are net sinks of CO2. Observations are required to identify these regions and the ocean processes that control their behavior.

Air-Sea CO2 Flux Trend 1990-2010

Anthropogenic air-sea CO2 fluxes. Ocean observations (red line and circles) compared with models (blue line with squares).

• Large-scale patterns of natural climate variability, such as El Niño, are known to significantly alter regional air-sea exchange of CO2.

• In order to project the future capacity of the ocean to sequester anthropogenic CO2 emissions it is necessary to elucidate the processes that influence air-sea exchange rates and to better understand how those processes might vary as the Earth’s climate changes.

• A consequence of ocean uptake of CO2 is acidification of the ocean, with potentially significant impacts on marine biota.