Research Product

The oceans continue to absorb CO2 in step with the increasing atmospheric concentration of CO2. The dissolved CO2 reacts with seawater to form carbonic acid (H2CO3) and liberate hydrogen ions, causing the pH of the oceans to decrease. Ocean acidification is thus an inevitable and tangible consequence of rising atmospheric CO2 that will impact marine ecosystems on a global scale. However, at local scales, the severity of acidification – that is, the magnitude and rate of decrease in pH – is the result of a number of physical, chemical and biological factors acting in combination. Consequently, ocean acidification “hotspots” can occur at spatial scales of tens to hundreds of kilometers and are believed to be products of (1) globally increased atmospheric CO2; (2) non-uniform changes in circulation and biological processes; and (3) local pollution and runoff sources that exacerbate the effects of ocean acidification in the coastal marine environment. The relative influence of these factors and their interactions vary over space and time, but local, non-CO2 sources may account for over half of the drop in pH observed in some estuaries. Despite the global scale of ocean acidification, the most immediate danger to ecosystems and human benefits derived from those ecosystems may stem from the additive effects of global change and local drivers that impact the coastal ocean. The potential biological, ecological, and socioeconomic impacts of acidification are thus poised to play out in a nonrandom way in the Earth’s coastal oceans, affective nearshore environments and ecosystem services that over half the world’s population depends upon. Effects of local inputs on pH levels and aragonite saturation state (a correlate of ocean pH that influences CaCO3 stability in shell-producing organisms) in nearshore waters may be detrimental to sensitive species and ecosystem health by reducing the growth rate and/or ability of shell producing organisms to form aragonite shells. The impacts of acidification may be especially harmful in concert with other stressors in the coastal ocean, such as overfishing, habitat destruction, warming oceans and pollution. While elevated atmospheric CO2 requires far-reaching solutions, a variety of local actions have the potential to mitigate some of the non-CO2 stresses. In the United States, many of the necessary legal and policy tools to address these local stresses are already in place