A changing ocean: decision-making in the face of multiplying ocean stressors

© Meredith Kurz

Let yourself dive into the hottest ocean science issues through the eyes of women that have dedicated their lives to oceanography, and who are currently sharing their latest scientific findings at the 4th International Symposium on the Effects of Climate Change on the World’s Oceans, ECCWO (Washington D.C., USA, 4-8 June) – a gathering of leading ocean and climate researchers from more than 50 countries.

Our interviewees offer us a warning about just how much is at stake when it comes to the conservation and sustainable use of the ocean in a changing climate, but they also highlight how the scientific community can play a significant role in bridging the gap between knowledge and action.

Thanks to a growing body of science, exciting innovations and discoveries, we now have a greater understanding of our planet’s climate system – but how do we turn decision-relevant knowledge into concrete steps toward delivering the ocean we need for the future we want? We asked Meredith Kurz and Dr. Elizabeth “Libby” Jewett from the U.S. National Oceanic and Atmosphere Administration (U.S.-NOAA) to explain why this is crucial to decision-makers and society at large.

Today what are the main factors changing the (chemical, physical, etc.) state of our ocean?

The primary factor driving the global decrease in average seawater pH and the global increase in ocean temperature is anthropogenic (human-induced) CO2 emissions. As the concentration of CO2 in the atmosphere increases, so did the amount that the ocean absorbs. The ocean has absorbed over a quarter of CO2 emissions since industrialization began. A predictable result of this rise in CO2 dissolved in seawater is a chemical reaction which lowers the pH of the water – and as a result, average seawater acidity has already increased by almost 30% since the early 20th century. Together, both ocean warming and ocean acidification form the two “CO2 problems” which are the primary drivers changing the global state of the ocean.

However, CO2 emissions are not the only human activity that can affect seawater chemistry, which can vary across time and space. For example, ocean acidification along the coast is more variable than in open waters. Runoff from land can contain nutrients that, through various mechanisms, can affect the local seawater chemistry, causing both low oxygen and acidification. The amount of rain in a given region also impacts the local pH because freshwater has a naturally low pH. Other industrial gasses such as sulfuric acid can also acidify coastal waters through local deposition. Identifying the multiple stressors that vary across space and time is an important priority for ocean acidification researchers.

How would you explain ocean acidification and its threat to a politician / your local councilor?

Ocean acidification is sometimes called “the other CO2 problem” because it is directly caused by CO2 emissions, and we have already seen significant changes to the global ocean. To understand why acidification is bad for the ocean, we can simply look at why your dentist will tell you that carbonated soda is bad for your teeth: adding carbon dioxide to water reduces the pH of that water. The ocean water will never be as acidic as soda is, but researchers fear that marine ecosystems will not have time to adapt to this rapid change in pH. A more acidic ocean means that shellfish and corals have more difficulty in building their shells and skeletons, because the particles required (carbonate ions) are less available. In some of the more acidic parts of the ocean, we have already seen holes developing in the shells of tiny organisms called pteropods. These organisms form the base of food chains that include fish and marine mammals that are important to humans.

Coral reefs form critical habitat for many marine organisms and therefore have a massive economic value, in addition to their value as tourist destinations and culturally significant ecosystems. Although the biggest threat faced by coral reefs in the near term is bleaching, which is caused by heat, ocean acidification can make it harder for reefs to recover from bleaching. Ocean acidification could also have very surprising effects, such as changing the taste of shrimp!

Ultimately, ocean acidification is not just a threat to baby oysters and corals. It is a threat to human food security and, therefore, our wellbeing.

How can scientists around the world collectively measure changes in the ocean? What are the main systems in place? Are they enough?

Starting in 2012, scientists from around the world met in Seattle, USA, and then in St. Andrews, UK, to envision a Global Ocean Acidification Observing Network (GOA-ON) which has since been established. The purpose of these meetings was to agree on a collaborative, cohesive international approach to tracking ocean acidification and understanding its impacts. Researchers who study acidification agreed that the best approach is to work along local, regional, and global scales.

Researchers who met as part of GOA-ON agreed that four carbon-related measurements provide the minimum level of information about the carbonate chemistry of ocean water: pH, dissolved inorganic carbon, total alkalinity, and carbon dioxide partial pressure (or fugacity). Scientists need to measure at least two of these to be able to calculate the four measurements. When taken together with salinity, temperature, pressure, and oxygen concentration, scientists can create a complete picture of the physical and chemical state of a particular location in the ocean at a particular time.[1]

Ocean acidification researchers use a variety of platforms to gather data on ocean chemistry, including ship-based sampling on research cruises or “ships of opportunity,” fixed platforms like piers and moorings, or mobile platforms like robotic marine gliders. Scientists can attach sensors to gather key data through these platforms. Ideally, scientists take these measurements frequently over time, because ocean chemistry can vary seasonally or even over the course of a day, so a single measurement is not enough to provide an accurate picture. One of GOA-ON’s goals is to provide a data portal that shows the world’s ocean acidification observation assets.[2] It shows that while ocean acidification observations are spreading, there are some significant gaps in several regions, particularly places that are harder for researchers to get to like the Southern Ocean or the Arctic.

How do we tell natural from human-induced changes in the ocean? To what extent does climate change exacerbate natural ocean stressors?

Teasing apart natural from anthropogenic changes in the ocean is tricky. However, the chemistry of ocean acidification is very straightforward and can be demonstrated in a classroom by blowing CO2 (as we exhale) into a tank of water. Simple chemistry tells us that CO2 combines with H2O (water) to form carbonic acid (CH2O2) – that’s why we call it ocean acidification. Active research is underway to tease apart the carbon dioxide coming from the burning of fossil fuels and other human activities, from the carbon dioxide that naturally appears as a byproduct of biological respiration. To further complicate the work of scientists, biological respiration can also be enhanced by climate changes.

Is there anything in particular that citizens can do in their everyday lives to help?

Ocean acidification is caused by CO2 emissions, which means that the global community can address it the same way that it is addressing climate change: by reducing CO2 emissions. Individuals can calculate their carbon footprint and identify the best ways to reduce their personal emissions, like choosing to bike or take public transportation to work instead of driving a personal vehicle. Communities have more power to help, because they can work together to create solutions like asking their public officials to build more renewable energy sources to replace energy from fossil fuels in their community. There are other ways to help besides reducing emissions, because ecosystems have a harder time coping with ocean acidification when it is combined with other stressors to the ocean.  Working to reduce nutrient pollution entering the ocean from land, such as using less fertilizer on lawns, can reduce a locally manageable stress on the ocean, giving marine ecosystems more capacity to cope with ocean acidification.


UNESCO’s Intergovernmental Oceanographic Commission (IOC) has co-organized the quadrennial International Symposium on the Effects of Climate Change on the World’s Oceans since 2008 in collaboration with the International Council for the Exploration of the Sea (ICES), the North Pacific Marine Science Organization (PICES), and the Food and Agricultural Organization of the United Nations (FAO).

Follow all ECCWO news on Twitter at @ECCWO!

For more information, please contact:

Salvatore Arico (s.arico(at)unesco.org)

Libby Jewett (libby.jewett(at)noaa.gov)

Meredith Kurz (meredith.kurz(at)noaa.gov)

Or visit:

ECCWO Symposium website

The United Nations Educational, Scientific and Cultural Organization Intergovernmental Oceanographic Commission, 8 June 2018. Press release.

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