Carbon Sequestration and the Ocean: How will our waters react?

Carbon sequestration, ocean acidification, and global climate change: these are just a few complex processes associated with the carbon cycle and ultimately, the future of our environment. More familiar and accessible to the general public, however, is the fact that the amount of atmospheric carbon, a primary driver of climate change, is steadily on the rise in today’s world. Questions and concerns on the future of our planet develop when we begin to contemplate what consequences will arise as a result of this increased carbon. How will nature react?

Before diving deeper, let’s first try to understand the carbon cycle. Carbon is an element basic and vital to all life found in both living and non-living things. Carbon “sources” release the element either into the environment or into another form, whereas “sinks” take in and store carbon. This movement through sinks and sources creates a stop-and-start flow where time is inconsistent; carbon can be stored for millions of years in a rock or for only a day in a plant leaf before it may be eaten and released once again through animal respiration.

The carbon cycle is a system, an intricate web of parts working in relation to one another. When one part of a system is altered others may shift in an effort to restore balance. Through burning fossil fuels, humans are releasing massive amounts of carbon into the atmosphere that would otherwise be locked up and stored in the geosphere (mainly rocks and sediment). It is primarily excess carbon in our atmosphere that is giving the planet a high fever. Considering that the ocean acts as a carbon sink and covers 71% of the earth’s surface (and is 270 times greater in mass than the atmosphere!), the importance of understanding its role in regulating future changes in the environment becomes evermore apparent.

In the ocean, carbon sequestration, a fancy word for the process by which carbon dioxide is removed from the atmosphere, is achieved through various chemical and biological processes. Plankton at the ocean surface use photosynthesis to convert carbon dioxide into sugars in the same way trees and land plants do on land. Sea creatures consume this phytoplankton (photosynthesizing plankton), and therefore the carbon containing sugars, eventually dying and sinking to the bottom of the unfathomably deep ocean, locking the carbon away over millions of years as sediment. While chemical process can create calcium carbonate in the water and some organisms use carbon to build shells and skeletons, it is the “biological pump” initiated by surface-water plankton that is the primary driver of oceanic carbon sequestration.

A recent study conducted by the California Institute of Technology on the Southern Ocean has shown that higher phytoplankton efficiency, and therefore greater carbon sequestration, is actually associated with periods of colder climates over the past 40,000 years. Why? The answer is a seemingly unlikely candidate that begins with nutrients. A healthy population of phytoplankton relies on nutrients like nitrogen, phosphorus, and iron in order to thrive, essentially depleting these sources to run at optimal efficiency. In the modern Southern Ocean, researches have noted that the biological pump is not working at such “optimal efficiency” despite available nitrogen and phosphorus. The culprit: a limited source of iron. Through an additional analysis of over 10,000 fossils, an international team of researchers was able to look into the past, compare with the present, and conclude that colder climates have allowed more biomass to grow in the surface Southern Ocean, and it is likely because of the consequential stronger winds bringing more iron in from the continents to the ocean.

What makes this new finding so compelling is what it may imply for warmer climates as opposed to cold. Will an increasingly warmer climate experience decreasing levels of carbon sequestration if the opposite is true? This research has given us critical information in terms of how our biological pump, the photosynthesizing, carbon sequestering plankton, may change in response to a warmer climate. It seems that they may be less efficient at taking in the increasing amounts of carbon, which may heat the atmosphere further to create a vicious feed-loop.

Such research demonstrates the complexity of our ocean and its response to carbon, a building block of life. It sheds light on processes other than ocean acidification, which has been getting most attention in terms of oceanic and climate change research (as it should!). And while gaining insight on how the oceans will respond to the human derived influx of carbon to the atmosphere is imperative, it is equally important to conduct research on and devise methods to actively mitigate increased levels of atmospheric carbon.

Another recent scientific investigation published in the journal Frontiers in Ecology and the Environment has offered new information that may help us do just this, mitigate carbon influx. The team’s analysis shows that shoreline environments, such as mangroves, sea grasses, and tidal marshes, show more promise for mitigating climate change than any other ecosystem. Our planet’s coastline is extensive enough to wrap around the earth almost fifteen times (372,000 miles!). The study found that annually, such ecosystems could trap and store 2 to 35 times more carbon than even ocean phytoplankton. The major issue lies in current state of these ecosystems; within only the past 50 years, 50% of the world’s mangrove forests have vanished due to anthropogenic action. With this information, the potential for positive change by human effort is clear. In addition to switching from reliance on fossil fuels, to driving fewer cars, there are other actions we can take. We push for habitat restoration and use research to help us combat our ecological footprint.

The oceans cannot fight carbon alone- we must look into all aspects of our complicated, complex environment in order to find solutions. Are you willing to help take action?

KAYLA DELVENTHAL

References:

Derouin, S. (2017), Study finds that coastal wetlands excel at storing carbon, Eos, 98, https://doi.org/10.1029/2017EO069971. Published on 16 March 2017.

Deep-sea coral evidence for lower Southern Ocean surface nitrate concentrations during the last ice age, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1615718114