Ocean Acidification 101

Across the globe, carbon emissions from burning fossil fuels are changing the Earth’s atmosphere. But it’s not just our atmosphere that’s affected—our oceans are feeling it, too, through a process called ocean acidification (OA).

What Is Ocean Acidification?
Carbon dioxide (CO₂) is a trace gas, meaning it makes up less than 1% of the Earth’s atmosphere. At the same time, it’s a powerful greenhouse gas, and it plays a vital role in regulating the planet’s surface temperature by trapping heat. Since the Industrial Revolution, the level of atmospheric CO₂ has climbed steadily due to human activity, such as driving gas-powered vehicles and heating our homes. Most scientists agree that this increase in CO₂ is behind the current episode of global climate change.

So, how does more CO₂ in the atmosphere affect the oceans? Well, oceans absorb huge amounts of CO₂—about 28% of our excess emissions. Once taken in by the ocean, CO₂ goes through a series of reactions that change seawater chemistry. As a result, the ocean has become 30% more acidic over the past 250 years. And as we pump more of this greenhouse gas into the atmosphere, we’re driving the pH of ocean water lower and lower, making it more and more acidic. (Note: Acidity increases as the pH decreases.) Thus, ocean acidification is a progressive increase in the acidity of the ocean over time.

Effects on Ocean Life
Ocean acidification threatens how marine ecosystems function by making a compound called carbonate scarce. Carbonate is a key compound used by animals like corals, lobsters, crabs, clams, oysters, and other shellfish to build their shells and skeletons. The acidified water can threaten certain tiny plankton and larvae that depend on the carbonate ion, too. This threatens the health of the ocean food web.

People depend on the ocean for food, water quality, storm buffering, and many other important functions. Ocean acidification is yet another stress, along with rising temperatures, eutrophication, habitat destruction, and sea level rise, on marine environments that may endanger the flow of goods and services to marine-dependent communities. Disruptions to marine ecosystems can alter these relationships.

How the National Park Service Addresses Ocean Acidification
In a recent survey of parks, staff were asked to rank emerging and cross-cutting issues that will affect or are already affecting park water resources. In ocean parks, OA is the second highest priority issue, coming in just under energy development.

Some parks have taken the initiative to conduct OA work. Here is a brief summary of the OA work happening in many of our ocean and coastal parks.

Alaska Region: MODELING. Alaska Region partnered with Glacier Bay National Park and the University of Alaska Fairbanks to develop an OA model for the region. This is a systems-based approach to a conceptual model of OA focusing on trophic linkages between nearshore coastal communities and nearshore coastal dynamics, with consideration for the physio-chemical characteristics and biology found in Alaska coastal national parks. Some areas of the Arctic are already corrosive to shells of marine organisms, and most surface waters will be within decades. This will affect ecosystems and people who depend on them.

Glacier Bay National Park: EXPERIMENTATION, OCEANOGRAPHY, AND TROPHIC ECOLOGY. Over the past two centuries, Glacier Bay has experienced rapid retreat and melting of its numerous glaciers, leading to an increase in the amount of freshwater entering the marine ecosystem. This input of low-alkalinity freshwater has reduced the surface water’s ability to resist decreases in pH, especially during seasons when glacial runoff is high (summer/fall). Glacier Bay partnered with the University of Alaska Fairbanks to conduct a project from 2011 – 2013 investigating freshwater input effects on OA in a glacial fjord system. Building on the knowledge gained from this project, a new 2016–2018 project will investigate the potential correlation between OA to effects on zooplankton health within the same glacial fjord system in Glacier Bay.

Dry Tortugas and Biscayne National Parks: CORAL REEFS AND CALCIFICATION RATE MONITORING. The U.S. Geological Survey is monitoring calcification rates in coral reefs in Dry Tortugas, Biscayne, and Buck Island national parks. The goal of this work is to establish baseline calcification rates for corals and calcareous algae and determine how they respond to increased OA. Laboratory experiments predict that rates of reef-building organism calcification will decline markedly in the first half of the 21st century.

Acadia National Park: MONITORING OCEAN ACIDIFICATION, EXPERIMENTS, AND CITIZEN SCIENCE. Acadia National Park is working with the Schoodic Institute and other partners to investigate the impacts of climate change and OA on our intertidal ecosystems. Acadia deploys sensors in the water and engages professional scientists and citizen science volunteers to study physical changes (pH, temperature, dissolved oxygen), changes in the abundance, distribution, and phenology of intertidal species, and changes in species interactions (e.g., predator-prey). Since it will take time to get results, the park is using scenario planning to identify best actions as monitoring information becomes available.

Currently, the NPS does not have a national OA monitoring network. It would be beneficial to incorporate OA into long-term marine monitoring programs to document the degree of OA in park units and to interpret changes in biotic community structure monitored as part of these programs. This network would provide a better understanding of the temporal and spatial scales of variability in ocean carbon chemistry and biology and the observational basis for developing predictive models for future changes in OA and its consequences for marine ecosystems. National parks are ideal sites for an OA demonstration project because of their natural resources, scientific staff, and support infrastructure. We look forward to building an OA monitoring program for parks in the near future.