Ocean acidification involves the ongoing decrease in the pH of the Earth’s oceans. This change in ocean chemistry is primarily a result of the ocean absorbing increased amounts of atmospheric carbon dioxide (CO2) from human activities, such as the burning of fossil fuels and deforestation. Understanding and predicting ocean acidification and its potential impacts on marine ecosystems requires tools. Ocean acidification models provide scientists with the means to simulate oceanic processes and project future conditions.
What Are Ocean Acidification Models
Ocean acidification models are computer simulations and mathematical representations that mimic the ocean’s chemical and physical processes. They simulate changes in ocean chemistry driven by the absorption of atmospheric carbon dioxide. These models operate across various spatial scales, from global simulations to regional and local models examining specific coastlines or marine environments. Some models also incorporate coastal processes like nutrient runoff and upwelling, which influence local acidification levels.
The models represent the ocean’s carbon cycle, tracking how CO2 is taken up and the subsequent changes in chemistry. This includes dissolved inorganic carbon (DIC), which exists as carbon dioxide, bicarbonate, and carbonate, and understanding their balance. These efforts respond to the observed 26% increase in ocean acidity globally over the past 250 years.
How Models Function
Ocean acidification models integrate various data inputs and apply mathematical equations to simulate chemical reactions and physical processes within the ocean. Key data inputs include atmospheric CO2 levels, which have been steadily rising, reaching nearly 400 parts per million (ppm) from a pre-industrial level of 280 ppm. Other inputs encompass ocean currents, temperature, and salinity, as these factors influence CO2 absorption and distribution within the water column.
Once CO2 dissolves in seawater, it forms carbonic acid (H2CO3), which then dissociates into bicarbonate (HCO3-) and hydrogen ions (H+). The accumulation of these hydrogen ions increases the ocean’s acidity, lowering its pH. Models use equations to represent these chemical equilibria, such as CO2 + H2O → H+ + HCO3-, and track the resulting changes in pH and the availability of carbonate ions. The models are then validated against real-world observations, such as satellite data on sea surface temperature and salinity, to refine their accuracy and predictive capabilities.
Key Discoveries from Modeling
Ocean acidification models have yielded insights and predictions regarding future ocean conditions. Projections indicate a continued decrease in ocean pH, with some scenarios suggesting a reduction of 0.3 to 0.4 units by 2100, representing a 150% increase in acidity compared to pre-industrial times. This change directly impacts the saturation states of calcium carbonate minerals, particularly aragonite, a form of calcium carbonate used by many marine organisms to build shells and skeletons. Models project that surface waters in the Arctic and Southern Oceans could become undersaturated with aragonite within decades, making them corrosive to shell-forming creatures like pteropods.
These models also reveal potential impacts on marine organisms, especially calcifying species such as corals, shellfish, and certain plankton. As pH levels drop, it becomes harder for these organisms to form and maintain their shells and skeletons, potentially leading to reduced calcification rates, increased dissolution of existing structures, and impacts on growth, reproduction, and survival. For instance, some tropical and subtropical coral reefs are projected to lose 43% of their suitable habitats, and shellfish species could lose 13% of their global coastline habitats. Models have also shown that ocean acidification can affect the behavior of non-calcifying organisms, such as decreasing the ability of some fish to detect predators.
Using Model Insights
The findings from ocean acidification models are applied in various ways to address this environmental challenge. These insights inform policy decisions by providing projections of future ocean chemistry changes under different emission scenarios. For example, policymakers utilize model outputs to understand the scope of the problem and to develop strategies aimed at reducing CO2 emissions through international agreements such as the Paris Agreement.
Model insights also guide conservation efforts by identifying ecosystems and species most vulnerable to acidification, allowing for targeted protection and management strategies. This includes informing the management of fisheries and protected marine species, as models can capture the effects of ocean acidification on entire ecosystems. Model projections also direct further scientific research by highlighting areas where more understanding is needed, such as the cascading impacts throughout marine food webs. The continuous development of coastal forecasts for regions like the West Coast and Chesapeake Bay demonstrates the commitment to turning current observations into actionable predictions for adaptation and preparation.