Ocean acidification describes the ongoing decrease in the pH level of Earth’s oceans. This widespread change in ocean chemistry is a direct consequence of human activities, representing a significant alteration to the marine environment.
The Source of Ocean Acidification
The primary driver of ocean acidification is the ocean’s absorption of excess carbon dioxide (CO2) from the atmosphere. This CO2 largely originates from human activities such as the burning of fossil fuels, deforestation, and industrial processes. Approximately one-third to one-half of the CO2 released into the atmosphere since the Industrial Revolution has been absorbed by the oceans.
When CO2 dissolves in seawater, it reacts with water (H2O) to form carbonic acid (H2CO3). This carbonic acid then dissociates, releasing hydrogen ions (H+). The increased concentration of these hydrogen ions lowers the ocean’s pH, making it more acidic.
Effects on Marine Life
Increased ocean acidity poses a direct challenge to marine organisms, particularly those that build shells or skeletons from calcium carbonate. These calcifying organisms include corals, clams, oysters, sea urchins, and various types of plankton. The elevated hydrogen ion concentration in the water reduces the availability of carbonate ions, which are the building blocks these creatures need.
This reduction in carbonate ions makes it more difficult for organisms to form new shells and skeletons. Existing shells and skeletons can also corrode or dissolve under more acidic conditions. For instance, young oyster shells may struggle to form, and corals may find it harder to generate sturdy skeletons.
Consequences for Ocean Ecosystems
The harm to individual marine organisms can trigger widespread ripple effects throughout entire ocean ecosystems. Coral reefs, for example, provide habitat and shelter for thousands of other marine species. The decline of these foundational coral structures due to acidification threatens the biodiversity and stability of these complex ecosystems.
Impacts on plankton, which form the base of many marine food webs, can also have far-reaching consequences. For instance, pteropods, small sea snails, are a primary food source for larger animals like fish and whales in Arctic waters, and their shells are vulnerable to dissolving in more acidic conditions. A decrease in these microscopic organisms can disrupt the entire food chain, affecting the survival and abundance of species higher up, including commercially important fish and shellfish.