Coastal systems tend to be an order of magnitude more variable than open 
ocean systems in terms of physical and biogeochemical processes. As a 
result sampling programs designed for open ocean systems may not accurately 
characterize coastal environments, can provide a biased view of the 
contribution of these systems to the global carbon cycle and for the 
purposes of this program, to atmospheric carbon dioxide concentrations 
over North America. The North American Carbon Experiment will therefore 
clearly require a program focused on understanding the role of coastal 
systems have in affecting atmospheric CO2 distributions.  

Episodic and seasonal nutrient injections, through upwelling and riverine 
input, support high rates of primary productivity that contribute 
significantly to carbon export from surface waters, across the continental 
shelf and into the deep ocean.  At the same time the upwelling of deep 
cold water, enriched in CO2 as a result of the respiration of settling 
particles, may represent a localized source of atmospheric CO2. Even if 
the net air-sea CO2 flux, resulting from deep-water ventilation and 
biological productivity, may be close to zero, the spatial and temporal 
decoupling of these two processes can produce transient gradients in 
atmospheric CO2 in the atmospheric boundary layer of coastal regions.   

The spatial and temporal separation of sources (upwelling nutrients) and 
sinks (primary production) act to extend the size of the coastal domain 
further from shore. Other processes such as the production and consumption 
of dissolved organic matter and denitrification also can extend the 
influence of coastal processes well into the ocean interior. As mentioned 
previously climatic variability strongly regulates the size of the 
productive domain (see Chavez et al., in press for the effects of 
El Niņo on the west coast of north America). The size of the coastal 
footprint can then vary from 50 to 500 km from shore or by an order of 
magnitude depending on environmental conditions. Under certain conditions 
the contributions of coastal areas, normally considered to be small 
relative to open ocean regions because of areal extent, to global budgets 
may be significant and underestimated.