The level of global atmospheric CO2 is now approaching 400 parts per million (ppm) – an increase of over 40% from the pre-Industrial Revolution level. This is largely a result of the release of geologically-stored carbon through the burning of fossil fuels, and also changes in the use of land. From a geological perspective, it is happening in an instant. The oceans absorb about a quarter of these emissions, and current atmospheric CO2 levels would be even higher but for this.
The downside of this oceanic uptake is that CO2 reacts with water to form carbonic acid and thus decreases the pH level of seawater, a process referred to as ocean acidification. Since pre-industrial times, the pH of the global surface ocean has decreased from 8.2 to 8.1 (equivalent to a 30% increase in the concentration of hydrogen ions), and it is predicted that with business-as-usual trends, the pH level could drop to 7.9 by the end of the 21st century. There are widespread concerns as to how marine organisms, especially calcifiers such as shellfish and corals whose ability to build calcium carbonate shells and skeletons can be impaired by ocean acidification, can adapt to a rapid rate of change probably not evident in the last 55 million years.
The implications for marine ecosystems that will be subjected to this stress – alongside others such as climate change – and for the key services these ecosystems provide to mankind need to be elucidated. Research to date suggests complex biological responses can be expected with potential winners and losers, but proxy studies such as those on high C02 environments around cold water volcanic seeps and paleo-studies serve to underline the concerns.
In this context it is essential that coordinated long-term ocean acidification monitoring is undertaken to assess variability and trends in the ocean carbon system and support assessment of the risks to and impacts on marine ecosystems and services. Ocean acidification is influenced by physical, chemical, and biological processes which lead to spatial and temporal variability on a range of scales. Knowledge is needed in order to understand the current conditions to which marine organisms are exposed and to help distinguish long-term anthropogenic acidification from natural variability and cycles. However, monitoring the marine carbonate system is not a trivial task, and relies on the diligent work and studies of several groups.
The ICES Cooperative Research Report on Chemical aspects of ocean acidification monitoring in the ICES marine area originated from the Marine Chemistry Working Group's (MCWG) contribution to ICES advice to OSPAR on this topic. The report considers and makes recommendations on the approach and tools available to achieve coordinated monitoring of changes in the carbon system in the ICES marine area, i.e. the Northeast Atlantic and Baltic Sea, and outlines current monitoring activities in the region.