The oceans have an important role in controlling Earth's climate. It is also an important sink for greenhouse gases such as Carbon Dioxide (CO₂). CO₂ is continuously exchanged between the atmosphere and the ocean. Overall, the ocean absorbs more carbon dioxide than it releases to the atmosphere. In this way, the oceans act as a carbon "sink". Concerns about future global climate change due to the increases amount of CO₂ in the atmosphere has pressured scientists to find out more about the ocean carbon cycle. Our research at BIOS focuses on understanding the biological, chemical and physical processes that control the ocean carbon, nitrogen and sulphur cycle; physical and biological processes influencing oceanatmosphere gas exchange of CO₂; coupling between ocean biogeochemical processes and climate variability; and influence of coral reefs and calcifying organisms on ocean carbon cycling and the exchange of CO2 between the ocean and the atmosphere.

The trace amounts of carbon dioxide (CO₂) present in the atmosphere play an important role in biological, chemical and physical processes at the earth's surface, and its abundance is postulated as a major regulator of climate (e.g., IPCC, 1995, 2001). Since the industrial revolution, combustion of fossil fuels and changes in the mosaic of terrestrial ecosystems have contributed to the observed increase in atmospheric CO₂ (Figure 1) and growing concerns about climate change consequences (i.e., global temperature increases; Figure 2). Only half of the CO₂ released by human activities (anthropogenic CO₂) currently resides in the atmosphere, the remainder residing in mobile terrestrial and oceanic reservoirs (sinks of CO₂)(Figure 3). Although understanding of the global uptake and storage of CO₂ in the oceans and terrestrial biosphere has greatly advanced in the last 16 years, it has been recognized that there is a great need for a concerted effort to pursue global carbon cycle science in the next two decades (U.S. Carbon Cycle Science Plan, 1999; National Academy of Sciences, 2001). In response, federal agencies such as NSF and NOAA are committed to a national effort to "increase significantly our understanding of the processes that regulate the transport and transformations of carbon within and among the terrestrial, oceanic and atmospheric environments of the Earth".

A particular emphasis is improving the estimates of the oceanic carbon sink and the underlying mechanisms that regulate it. In the last decade, internationally coordinated marine research has greatly increased the ability to understand and model the ocean's complex biological, chemical and physical processes. Our knowledge of the uptake, storage, transport and transformation of carbon in the oceans has greatly improved through observations and model synthesis of CO₂ data, chemical tracers (e.g., radiocarbon, tritium-helium and halocarbon distributions, δ13C ratio) of ocean circulation, and "tracers" of biological processes (e.g., microbial-phytoplankton-zooplankton interactions and their modulation of carbon and nutrient cycling). A newly emerging challenge, one dictated by society's need to prepare for the impacts of global change on the Earth System and climate variability, is to develop a "quantitative and predictive understanding of marine biogeochemical cycles and ecosystems, their interactions in response to global change and feedbacks of ocean processes to the Earth System" (IMBER Science Plan, 2004). In 2004, as part of international efforts sponsored by IOC (International Oceanographic Committee)/SCOR (Scientific Committee for Ocean Research), two new projects (IMBER and SOLAS) will focus research on carbon cycling in the ocean, and the atmosphere-ocean interface. For example, there remains much uncertainty about the geographic and temporal variability of ocean carbon sources and sinks, and their modulation by biological and physical processes, particularly in the ocean basins adjacent to North America (Figure 4, Takahashi et al., 2002). The prediction of future atmospheric CO₂ concentrations and the impact on climate requires an in depth understanding of the natural feedback mechanisms that operate between the physical, biological and chemical components of the global climate system (IPCC, 2001; IPCC 4th Assessment, in preparation 2006).