Ocean Acidification and Climate Change

Sumedha B S, Bangalore University

The evil twin of climate change- Ocean acidification occurs due to an increase in concentrations of carbon dioxide in seawater. Carbonic acid is formed when Carbon dioxide dissolves in the seawater. This reduces the water pH.  Also, carbonate ion (CO32−) concentration decreases, which causes a reduction in the saturation state (Ω) of CaCO3 minerals. Calcium carbonate is present in 2 forms: Calcite (stable form), and aragonite (metastable). These CaCO3 minerals dissolve in seawater when Ω is less than 1. 

Ocean acidification has a negative socio-economical effect especially the subpolar regions like the Gulf of Alaska. Commercial fisheries of the Gulf of Alaska are of economic importance to US and Canadian harvesters. These have a high nutritional value for sustaining fishing communities. Here, a significant part of commercial fisheries include molluscs, shellfish, crabs, and salmons.

Ocean acidity depends on factors such as – 

˒ temperature fluctuations, 

˒ ocean mixing patterns, 

˒ acidic freshwater inputs, 

˒ input of nutrients from land sources and

˒ biological carbon drawdown.

The ocean salinity, Chlorophyll-a, nutrients, and oxygen greatly affects marine life. This chemistry in the Gulf of Alaska is strongly influenced by variations of oceanic conditions such as Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO). 

The recent Research: 

Typically, ocean acidification was thought of like this slow process that gradually changes the carbon chemistry of seawater. It is commonly assumed that CO2 partial pressure (pCO2) follows the atmospheric pCO2. This assumption breaks down due to variability in the internal Earth System. 

In the study, it was found that the chemical conditions of the marine ecosystem change on a daily and seasonal basis. In the Gulf of Alaska, the fluctuations of wind and ocean currents affected the rate of acidification. This fluctuation occurs despite the gradual trend of ocean acidification.

Hauri and her team used a model that combines physical, hydrological biogeochemical models. It had output from a 34-year regional ocean biogeochemical simulation for the Gulf of Alaska (1980−2013). 

They identified decadal fluctuations in chemical conditions. These were driven by the strength of the “gyre” of the North Pacific. “Gyre” is a system of circulating ocean currents associated with large wind currents. It strongly affects the Gulf of Alaska. 

If the gyre is strong, it brings deep water (rich in carbon dioxide) up, to the surface. This increases the rate of ocean acidification, causing stress to sensitive organisms. When gyre is weak, less carbon is brought to the ocean surface. This can reduce or reverse the ocean acidification effect. They also observed that every 5-10 years massive cycles occurred.

So, the climate-driven regional ocean fluctuations can affect ocean acidification rates in short timescales.  

The study was done by Hauri and her team at the University of Alaska and was published in Communications Earth & Environment.

The authors emphasized that more research is required to understand the effects of many simultaneous stressors. Also, to identify the interrelatedness of acidification and climate change. 

Hauri and her team’s efforts will provide much-needed information to commercial fisheries and local fishermen. This will help them to adapt and plan for the future.

Also read: Refrigeration-free COVID-19 vaccines are cultured on plants and bacteria

References: 

1. Hauri, C. (2021, September 15). Modulation of ocean acidification by decadal. Communications Earth & Environment. https://www.nature.com/articles/s43247-021-00254-z#citeas

2. https://phys.org/news/2021-09-natural-gulf-alaska-accentuate-ocean.html

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