Ocean ecosystems play a critical role in carbon storage and oxygen generation. Some of these ecosystems are under threat; others remain unexplored. Understanding how key players such as whales, plankton, seagrasses and other forms of sea life interact sheds light on Earth’s carbon cycle.
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Samuel Granados, Reuters |
HOW CARBON IS CAPTURED
Key to life
Carbon, a chemical element, is found in all organic matter on Earth, from the plants and animals alive today to fossil fuels buried underground.
It’s a key building block in the foods we eat, and in Earth’s most abundant greenhouse gases — carbon dioxide (CO2) and methane (CH4). Sunshine reflected off the planet’s surface back into the atmosphere causes those gas molecules to vibrate, warming the atmosphere. More CO2 leads to more warming, causing climate change.
The carbon cycle
Animals release carbon in the form of CO2 when they breathe, while plants take
in that gas along with sunshine to produce energy, a process called
photosynthesis.
Carbon dioxide also dissolves in seawater, where
it is absorbed by seagrasses and algae. Seagrasses, which are plants adapted
to live in the sea, are different from kelp and other algae in that they have
roots, veins, leaves — and even flowers and fruits.
Seagrass meadows
Seagrass meadows serve as excellent breeding grounds for sea mammals and habitats for baby fish. But scientists have estimated the world’s seagrass stocks are declining by about 7% per year.
For millennia, Earth’s natural systems kept carbon levels balanced in the environment. Industrial activities including the burning of fossil fuels, however, have increased atmospheric CO2 levels by nearly 50%, from 280 parts per million just over a century ago to about 417 ppm today.
That’s caused ocean CO2 levels to rise, making waters more acidic. But seagrasses can provide a buffer against that, too. By reducing the acidity of surrounding waters, seagrass ecosystems help protect animals with shells or external skeletons.
In the sunlit surface layer of oceans
Like land plants and seagrasses, microscopic marine algae known as phytoplankton also feed on CO2 and use photosynthesis to produce energy.
They live in both saltwater and freshwater environments, drifting freely with currents. And like plants, they also release oxygen, contributing at least 50% of the oxygen to Earth’s atmosphere.
CARBON IS TRANSFORMED
The food web
Seagrasses and phytoplankton near the ocean’s surface form the base of the aquatic food chain as they produce their own food, and then serve as food to others.
When carbon dioxide is consumed during photosynthesis, the carbon is incorporated in the phytoplankton and seagrasses, in the same way carbon is stored in the wood and leaves of a tree.
Carbon is then transferred to different layers of the ocean as primary producers are eaten by other organisms, which themselves reproduce, generate waste and die.
Body parts
Some plankton combine calcium and dissolved carbonates to form a calcium carbonate protective coating like the shells and other body parts of coral, clams or oysters.
Whales for example can absorb tons of carbon as their diet consists mainly of plankton and tiny shrimplike crustaceans called krill. A single whale can absorb around 33 tonnes, or 33,000 kilograms, of CO2 on average in its life while a tree can take in up to 22 kgs of CO2 a year.
Nutrient circulation
Phytoplankton, like land plants, require nutrients such as nitrate or calcium. They also need iron, which is scarce in large areas of the ocean. But when whales defecate, they release iron as well as other important nutrients like nitrogen in their feces.
The liquid plume then stimulates phytoplankton growth, attracting fish and other organisms in a phenomenon known as the “whale pump”.
CARBON SINK
Recycle
Crustaceans and fish transport carbon and nutrients by feeding in surface waters during the day and then migrating down the water column and excreting in deeper waters at night.
When critters die, the carbon and nutrients in their bodies either becomes part of the food chain or sinks to the ocean floor.
Carbon is stored
At the bottom of the ocean, bacteria works to decompose the carbon fixed in the soft and hard tissues of organisms. When mollusks and other carbon-rich organisms die, their shells and body parts can accumulate in ocean sediments, forming carbonate-rich deposits.
Locked away
Seagrasses also trap carbon in underwater sediments around their roots, stems and leaves.
The grasses store twice as much carbon per square mile as tropical forests do on land. As seagrasses die, the carbon gets locked into the sediment, where it can persist for thousands of years.
While covering only 0.1% of the ocean bed, seagrass ecosystems account for 10%–18% of the carbon buried in the oceans, according to a January 2020 study in the journal Frontiers in Marine Science.
When whale carcasses sink to the seafloor, the carbon in their carcasses can create a feast for deep-sea critters and also be buried in marine sediments.
Ocean deposits are by far the biggest sinks of carbon on the planet. After long periods of time, these deposits can alter physically and chemically to become rocks and sediments themselves.
Links
- Humanity’s Immense Impact On Earth’s Climate And Carbon Cycle
- Has World Started To Take Climate Change Fight Seriously?
- (USA) Manhattan’s Famous Digital Clock Is Now Counting Down To Climate Disaster
- Carbon Footprints Are Hard To Understand — Here’s What You Need To Know
- The World’s Climate Catastrophe Worsens Amid The Pandemic
- (AU) Carbon Road Map Winning Few Friends, Little Influence
- Experts Urge Further Climate Action As Lockdown Triggers 'Extreme' Emissions Drop
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