Ocean acidification/ CO2 monitoring

Ocean acidification, a decrease in seawater pH (acidity scale) caused by the increase of anthropogenic (human-induced) carbon dioxide (CO2) into the atmosphere, has received considerable attention in recent years. As scientists gain an understanding of the adverse affects of increased CO2 and decreased pH, a major concern of ocean acidification is the impact to organisms which use calcium to build their bones, skeletons or other structural components. Recent research has indicated that the oceans act as a net repository or “sink” for atmospheric CO2, but that this sink is not uniform worldwide. Many coastal regions oscillate between being a CO2 sink and source depending on the time of year. The effects of ocean acidification have yet to be fully understood in coastal regions were biogeochemical processes are often vastly different from regions dominated by upwelling.

The coastal areas surrounding our continent (continental margins) are known to play a considerable role in determining global carbon cycling; however, little has been done to determine input from the coastal margins towards the total carbon “budget.” Insufficient data exists to adequately determine the natural fluctuation (“flux”) of air-sea CO2 with any level of confidence. The ability to explain the control mechanisms driving the variability of coastal partial pressure of CO2 (pCO2 or the concentration of CO2 in seawater) and pH is limited. Understanding these control mechanisms and how they affect pCO2 and pH is essential to predicting future changes in CO2 flux, pH and carbonate saturation in our oceans. The primary reason that scientists are not able to determine the control mechanisms for coastal ocean regions is the absence of long-term high-resolution data. The highly dynamic coastal margin, with its combined terrestrial and oceanic input makes understanding this region a necessity for determining what mechanisms control the fluctuation of carbon dioxide.

Gray’s Reef National Marine Sanctuary (GRNMS), located in the South Atlantic Bight (SAB) along the southeastern United States is situated in a very unique and dynamic region. It sits along the divide between the inner and middle shelf with water depths in the 20 m range. The water at the sanctuary is primarily controlled by the middle shelf oceanic dynamics, but during heavy rain events, it can be affected by freshwater plumes coming from the numerous rivers along the Georgia and South Carolina coast. Temperature also plays a major role in the SAB pCO2 variability with seasonal changes being apparent. Recent research along the mid-outer shelf has suggested that the SAB is a CO2 net sink and the inner shelf acts as a net source releasing CO2 to the atmosphere. However, many factors such as ocean mixing, freshwater input, and Gulf Stream intrusions offer considerable input to the water chemistry at GRNMS.

Dr. Scott Noakes (The University of Georgia Center for Applied Isotope Studies), National Marine Sanctuaries, 15 May 2010. Full article.

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