Carbon dioxide and other greenhouse gases play a critical role in regulating the earth’s climate by keeping in heat that would otherwise escape to space - the greenhouse effect. Each year, human activities produce an additional 7 billion tons of CO₂. The portion of that additional “anthropogenic” CO₂ which stays in the atmosphere, amplifies the greenhouse effect, leading to a warmer climate. Because oceans absorb almost 50% of the CO₂ mankind produces each year, they serve as natural “sinks” to remove the gas from the air.

RSMAS researchers study the role of the ocean in the global carbon cycle. Some scientists inventory CO₂ levels at many ocean sites and track changes with time. By returning to specific places at different times of the year, these researchers can investigate the chemical dynamics of this CO₂ absorption process, to help predict future global warming (Figure 1). The exchange of carbon between the atmosphere and ocean can also be inferred using satellite data, which gives a global picture (Figure 2).

Figure 1: Representative section anthropogenic CO₂ (_mol/kg) in the Atlantic ocean. Note the deeper penetration of CO₂ in the north Atlantic (right) due to deep water formation (from Sabine et al 2004).

Figure 2: Global air-sea CO₂ flux based on QuikScat satellite measurements of surface roughness for 23-Feb-2001 (from Bogucki et al, 2005).

Other scientists study the small scale processes that govern the local exchange of CO₂ across the air-sea (Figure 3). An improved parameterization of local air-sea gas transfer, along with satellite derived data will lead to better estimates of the global CO₂ flux.

Figure 3 (left): Air-sea interaction spar buoy deployed during GASEX-2001 to measure CO₂ flux and controlling parameters.

Another focus is the investigation of means to increase amount of CO₂ entering the ocean. CO₂ in the ocean is used by phytoplankton whose abundance in often limited by the shortage of nutrients. Fertilizing the ocean with iron or other minerals could stimulate growth, thereby increasing CO₂ drawdown (Figure 4). Whether this would lead to permanent carbon removal or sequestration remains an active research topic.

Figure 4: Distribution of oceanic CO₂ 20 days after seeding with iron. Note the drawdown on CO₂ due to increased biological activity resulting from the introduction of iron, during the Southern Ocean Iron Experiment. From Hiscock et al 2003. (Figure from Frank Millero.)