Human Influence on Ocean Chemistry
Our oceans are changing. As we scroll through our news feeds, much of the current discussion centers on the assessment of the damage to the Texas coast and the aftermath of Hurricane Harvey. For good reason, too: the storm will likely be the costliest in United Stated history. In the coming weeks, the science community will try to interpret the degree to which a warmer ocean and atmosphere enhanced the storm. Climate change has become a household phrase, particularly in recent months with the United States withdrawal from the Paris Agreement.
Climate change is most commonly (and easily) associated with the progressive warming of our oceans and atmosphere in response to anthropogenic activity (e.g., fossil fuel consumption and changes in land use). The effects of a warming climate are tangible, easy to see, and easy to communicate (e.g., stronger storms, prolonged droughts, reduced sea-ice, and rising seas).
Each year humans release to the atmosphere more than nine gigatons of the heat-trapping greenhouse gas carbon dioxide (CO2). Around half of annual CO2 emissions remain in the atmosphere, about a quarter is absorbed by the terrestrial biosphere, and the remainder is absorbed by the surface ocean. The ocean’s absorption of CO2 represents the other, less talked about piece of the climate change puzzle. Ocean acidification (OA) is the progressive decrease in the pH of seawater caused by the uptake of CO2. Since the Industrial Revolution, average global ocean pH has dropped by 0.1 unit, which represents a 30% increase in acidity.
OA chemistry is well understood; it follows simple acid-base chemistry principles. As the surface ocean dissolves carbon dioxide, carbonate ions are consumed to buffer against changes in pH. Calcium carbonate minerals (calcite and aragonite) are the building blocks for many socioeconomically important marine organisms.
Building an Appreciation for OA
The concept of ocean acidification is not new; researchers in the 1940’s and 1950’s postulated that increasing atmospheric concentration of CO2 could alter the pH and saturation state, thus biological availability, of these important carbonate ions in the ocean. Perceptions of OA related risks began to change in the 1990’s as scientists increased their understanding of its impacts on tropical coral reefs, polar food chains, and all ecosystems in between.
These early findings resulted in dedicated funding from the United States, Europe, and elsewhere to further improve our understanding of processes that control OA. From this funding multi-national, multi-institutional programs such as the European Project on Ocean Acidification, BIOACID, UKOA, FOARAM Act/NOAA OA Plan, and others were conceived and stimulated a flurry of research and scientific publications addressing OA over the last two decades. Mathis et al. (2015) note that between 2000 and 2013, the number of scientific papers published on the topic increased by 35% per year, far out-pacing other scientific fields.
Merging Scientific Understanding and Policy
The rapid increase in knowledge and understanding of OA’s importance to coastal communities has moved the topic from a fringe issue to the mainstream, but has also shed light on its complexity especially when considered with other environmental stressors like changes in temperatures, deoxygenation, human modification of coastal habitat, and changes in coastal circulation and upwelling (Figure 1). The co-occurrence of multiple stressors in the natural environment complicates our much-advanced understanding of the short-term physical response of a single species to a single stressor such as the decrease in pH associated with OA, and presents a need for information at the population or ecosystem levels over longer time intervals.
This challenge points to the need for transdisciplinary science that requires engagement from those with expertise in many scientific fields. To provide realistic solutions to mitigate and cope with the rising threat of OA, the research community must transition to developing an understanding of the interactions of multiple stressors instead of single stressors, of physiological responses over years and decades instead of days and weeks, of impacts at the population and ecosystem level instead of a single species, and of the human perspective (e.g., mitigation and adaption) in the context carbon-cycle based research. The results of these exercises have begun and will continue to illustrate how complex ecosystems are responding to changing ocean chemistry, our vast socioeconomic dependence on the present state of coastal and open ocean chemistry, and the impact of OA on vulnerable human populations at local and regional levels.
With expected future population growth, economic growth will impose even greater pressure on an already stressed marine environment. Currently, economic growth is linked to human consumption of fossil fuels which further enhances the OA problem. Our current understanding of OA has begun to support evidence-based policy decisions. The foundation is in place.
As research continues, our understanding of how OA affects biological processes and subsequently ecosystems and socioeconomics will improve. As information gaps are filled by more transdisciplinary approaches to understanding OA, the science will become critical in informing future policy to protect vital marine resources. The OA story will be the subject of subsequent blogs. In them, we will examine the state of the science as it relates to either topical or regional understandings of OA.
Citation: Mathis, J. T., Cooley, S. R., Yates, K. K., & Williamson, P. (2015). Introduction to this special issue on ocean acidification: The pathway from science to policy. Oceanography, 28(2), 10-15.