Marine Carbon Dioxide Removal

Context: Majority of the efforts to fight climate change have been land-biased. The countries have invested heavily on land but underutilised the potential of oceans, seas, lakes, and rivers for carbon dioxide removal. 

Relevance of the Topic: Prelims- Marine Carbon Dioxide Removal, Ocean alkalinity enhancement, Ocean fertilization, Deep ocean biomass sinking.  

What is Marine Carbon Dioxide Removal?

• Marine Carbon Dioxide Removal (mCDR) is any ocean-based process or technique designed to remove carbon dioxide from the atmosphere and store it for long periods of time in the ocean. 
• Marine carbon capture strategies fall into two categories.
  1. Biotic approaches: Taking advantage of living systems like mangroves and macro-algae of our rivers to carefully calibrate biomass burial at sea. 
  2. Abiotic approaches: Manipulating physical or chemical properties, such as through ocean alkalinity enhancement (OAE), which are relatively more complicated.
• Other examples: Adding alkaline materials to the ocean to increase the amount of carbon stored in ocean waters; adding iron or other nutrients to ocean waters to increase phytoplankton growth and export of carbon to the deep ocean; and sinking organic materials, such as kelp or crop residue, into the deep ocean.

Why should oceans be focussed?

• Land saturation: Soils and rocks are so severely damaged that they no longer support efficient carbon capture. Land resources are also under severe pressure to support a huge population, agriculture, infrastructure etc. 
• Huge potential of Oceans: Sea and oceans have large surface areas (cover over 70% of the Earth's surface), thus better suited for CO2 absorption and removal. 

What is ocean alkalinity enhancement (OAE)?

• Ocean alkalinization is an approach to carbon removal that involves adding alkaline substances to seawater to enhance the ocean's natural carbon sink.
• How is it done?
  • Adding alkaline and/or basic solutions directly into seawater – using electrochemical methods to split ocean water into its acidic and basic components and then returning the basic components again to the ocean.
  • Adding certain types of mined alkaline minerals, such as olivine, to coastal and ocean waters. 
• Mechanism:
  • Adding alkalinity to seawater (or removing acid from seawater) would lead to a temporary elevation in seawater pH. 
  • This then results in a series of chemical reactions that convert dissolved carbon dioxide (already present in the seawater) into dissolved inorganic carbon, primarily in the form of bicarbonate (relatively stable form of carbon).
  • The seawater (now depleted in dissolved carbon dioxide) then takes up additional carbon dioxide from the atmosphere at the ocean surface. 
• Merits of OAE: 
  • Long-term storage of carbon in the form of stable bicarbonate ions. 
  • Provides the co-benefit of locally mitigating ocean acidification. 
  • Potential to enhance fisheries production. 

What is ocean fertilization?

• Ocean fertilization is a form of geoengineering that involves adding nutrients to the upper (sunlit) layers of the ocean to stimulate phytoplankton activity (photosynthesis) in an attempt to draw down atmospheric CO2 levels.
  • The transfer of carbon from the surface ocean to the deep ocean must result in a subsequent transfer of carbon from the atmosphere into the surface ocean.
• This could be accomplished by adding nutrients, such as iron, to the open oceans or nutrients may be moved from the deep ocean to the surface ocean through a process called "artificial upwelling.” 
• Ocean fertilization does not include conventional aquaculture, mariculture or the creation of artificial reefs. 

What is deep ocean biomass sinking?

• Deep ocean biomass sinking is the process of extracting carbon dioxide from the atmosphere through sinking carbon-rich biomass into the deep oceans.
  • Plants on land and in the ocean pull in carbon dioxide from their environment during photosynthesis. 
  • The carbon contained in terrestrial or marine biomass, such as crops or macroalgae, could potentially be sequestered from the atmosphere for long periods of time by sinking it in the deep ocean.