Skip to main content

Some Carbon Is Sequestered Semi-Permanently When It Is “Exported” to the Lower Levels of the Ocean

The ocean plays a pivotal role in the global carbon cycle, acting as one of the planet's major carbon sinks. Through processes such as the biological pump, the oceans can transfer carbon from surface waters to the deep ocean, effectively sequestering it for extended periods.[^1] This mechanism involves the transformation and transportation of organic material, commonly referred to as "marine snow," which includes particulate organic carbon (POC). These processes contribute significantly to long-term carbon storage in the ocean, potentially impacting global climate regulation.[^2]

Marine Snow and Particulate Organic Carbon (POC)​

Marine snow is a term that describes the continuous shower of organic material falling from the upper layers of the water column to the deep ocean. This includes dead organisms, fecal pellets, and other organic debris. When marine organisms die, their remains can either decompose near the surface or descend into the ocean depths. Similarly, the fecal matter produced by zooplankton and other marine animals contributes to this downward flux of organic material.

Particulate organic carbon (POC) is the form of carbon encapsulated within these particles. As POC sinks, it moves carbon away from the euphotic zone—the sunlit upper layer where photosynthesis occurs—and transports it to deeper ocean layers. This mechanism is significant because it removes carbon from the atmosphere-ocean exchange, sequestering it semi-permanently in the deep ocean. [^2][^3]

Sequestration Duration and Decomposition​

Once POC reaches the deep ocean, it can remain sequestered for hundreds to thousands of years. The cold, dark, and high-pressure conditions of the deep ocean slow down the decomposition process. Over time, microbial activity decomposes POC into CO2 and carbonic acids. In these chemical forms, carbon can persist in deep ocean waters for extended durations before being resurfaced by upwelling currents, which bring deep water back to the surface.[^2][^4][^5]

Uncertainties in Carbon Export and Sequestration​

Despite its importance, several uncertainties and complexities affect our understanding of carbon export and sequestration in the deep ocean:

  1. Rate of Carbon Export: The rate at which carbon is exported from the surface to the deep ocean is influenced by numerous factors, such as the types of organisms present, water temperature, nutrient availability, and the physical dynamics of the water column. Significant regional variation exists, and these factors are not fully understood.[^2]
  2. Efficiency of the Biological Pump: The efficiency with which the biological pump transports carbon to the deep ocean depends on the size, composition, and sinking rate of particulate matter. Larger particles tend to sink faster and are more likely to reach deep ocean layers before decomposing, while smaller particles are more susceptible to recycling in the upper layers.[^6]
  3. Impact of Ocean Acidification: The additional CO2 and carbonic acids introduced to the deep ocean raise concerns about ocean acidification. Increased acidity can affect the solubility of calcium carbonate, impacting marine organisms that rely on this compound for their shells and skeletons. Acidification can also alter marine ecosystem health, potentially disrupting the biological processes that drive the carbon pump.[^7]

Conclusion​

Marine snow and particulate organic carbon (POC) are fundamental to the sequestration of carbon in the deep ocean, playing pivotal roles within the biological pump mechanism. While these processes significantly contribute to long-term carbon storage, our understanding of the exact quantities of carbon exported to the ocean depths, the various influencing factors, and the safe potential for enhancing deep ocean carbon storage remains incomplete. Moreover, the challenges posed by increased ocean acidity, resulting from additional CO2 and carbonic acids, complicate this landscape further. These complexities highlight the ongoing need for detailed research to improve our comprehension and management of the ocean's role in the global carbon cycle.

Sources​

[^1]. Honjo, Susumu, et al. "Biological Pump and Ocean Carbon Sequestration." Oceanography, vol. 21, no. 3, 2008, pp. 1-8. [^2]. Boyd, Philip W., and Trull, Thomas W. "Understanding the Export of Marine Snow from the Upper Ocean." Biogeosciences, vol. 4, 2007, pp. 423-457.

  • Kwon, Eun-Young, Primeau, François, and Sarmiento, Jorge L. "The Impact of Atmospheric CO2 on Oceanic Carbon Sequestration." Nature Geoscience, vol. 2, 2009, pp. 563-566. [^3]. Turner, Jefferson T. "Zooplankton Fecal Pellets, Marine Snow, and Sinkers." Biogeosciences, vol. 11, no. 4, 2002, pp. 575-589. [^4]. Emerson, Steven, and Hedges, John I. "Processes Controlling the Organic Carbon Content of Open Ocean Sediments." Paleoceanography, vol. 3, no. 5, 1988, pp. 621-634. https://doi.org/10.1029/PA003i005p00621. [^5]. De La Rocha, Christina L. "The Biological Pump." Treatise on Geochemistry, 2003, pp. 83-111. https://doi.org/10.1016/B0-08-043751-6/06111-6. [^6]. Sigman, Daniel M., and Hain, Mathis P. "The Biological Productivity of the Ocean." Nature Education Knowledge, vol. 4, no. 4, 2012, pp. 1-16. [^7]. Riebesell, Ulf, et al. "Effects of Ocean Acidification on Marine Ecosystems." Annual Review of Ecology, Evolution, and Systematics, vol. 42, 2011, pp. 163-191.