Ocean Pastures Are The Most Important Part Of Global Carbon Cycle

Ocean Pastures Are The Most Important Part Of Global Carbon Cycle

In the ocean little goes to waste.  But even that waste is pure gold to oceanographer David Siegel, director of the Earth Research Institute at U.C. Santa Barbara.

Siegel and his colleagues study how oceans manage the vast majority of Earthly carbon emissions. They incorporated the lifecycle of phytoplankton and zooplankton — small, often microscopic animals at the bottom of the food chain —into a new mathematical model for assessing the global ocean carbon export. Their new model hopefully improves upon the many similar models that have gone before it.

The researchers used satellite observations to observe net primary production (NPP) which is easily seen as the “green” color of ocean plant life. That ocean green has been diminishing by staggering amounts over the past many decades, but at the same time scientific measurements and certainty about what is causing that collapse have been steadily improving. This is where ocean models can come into importance. Siegel and colleagues calculations provide them with estimates of net production of organic matter from aqueous carbon dioxide (CO2) by phytoplankton.

The scientists focused on the ocean’s biological pump, which exports organic carbon from the euphotic zone — the well-lit, upper ocean — through sinking particulate matter, largely from zooplankton feces and aggregates of algae. Once these leave the euphotic zone, sinking into the ocean depths, the carbon can be sequestered for a season or for centuries.


This graphic shows the global carbon budget with black arrows and values reflecting the natural carbon cycle and red the anthropogenic perturbation. Credit: 2007 IPCC report

“What we’ve done here is create the first step toward monitoring the strength and efficiency of the biological pump using satellite observations,” said Siegel, who is also a professor of marine science in UCSB’s Department of Geography. “The approach is unique in that previous ways have been empirical without considering the dynamics of the ocean food web.” The space/time patterns created by those empirical approaches are inconsistent with how oceanographers think the oceans should work, he noted.

Of course this is not the first instance of using such satellite data as the first satellites that sent back such data went into orbit in the early 1980’s. The satellites improved upon the prior method which often included scientists flying over vast stretches of ocean with a map in their lap making visual observations of NPP by mapping ocean color using these five ratings, “blue”, “blue-green”, “green”, “brown” and “red.” Correlating these colors with sea based measurements allowed the ocean scientists in the 1950’s through 1970’s to make, model and map NPP estimates for ocean regions. There is still a great deal of practical ocean science that can be effectively done using such simple “naturalists” methods in-spite of what the technology fixated ocean science community uses far more frequently.

Companies like Ocean Pastures Corp. now are working to fly its simple ocean color (b,bg,g,b,r) drones over their pastures where satellites are so frequently prevented by cloud cover from observing the ocean pastures. The low cost drones are able to fly low enough to be under the cloud deck and thus greatly increase the time during which ocean productivity data can be collected. When the skies are clear the OPC drones in combination with simultaneous satellite observations provide cross-calibration of the respective data sets. At the same time flying Slocum Gliders for undersea observations rounds out perfect science, in the merger of old and new.

Naturally best of all ocean productivity results (NPP) come from real time dynamic data gathering from multiple sources, satellites, airborne, in water multi-spectral data along with good old fashioned chemistry. This kind of real world ocean science is facilitated by having dedicated research ships on long duration ocean pasture studies such as the 2012 Ocean Pastures research in the NE Pacific. Ocean computer models are a great help but nothing holds a candle to hard data. “Data speak to me,” is the mantra of the experimentalist.

Carbon is present in the atmosphere and is stored in soils, oceans and the Earth’s crust. Any movement of carbon between — or in the case of the ocean, within — these reservoirs is called a flux. According to the researchers, oceans are a central component in the global carbon cycle through their storage, transport and transformations of carbon constituents. While it is known that the oceans cover 70+% of this planet the remaining 30% is not all suitable for plant life that fixes and stores carbon. Indeed less than 17% of the planets surface is capable of holding plant life, the rest is ice, and sand, and rock. Whereas almost the entire 70% of the planet that is ocean is a rich environment filled with, or at least capable of being filled with plant life, phytoplankton.

“Quantifying this carbon flux is critical for predicting the atmosphere’s response to changing climates,” Siegel said. “By analyzing the scattering signals that we got from satellite measurements of the ocean’s color, we were able to develop techniques to calculate how much of the biomass occurs in very large or very small particles.”


Shown are the links among the ocean’s biological pump and pelagic food web. Light blue waters are the euphotic zone, while the darker blue waters represent the twilight zone. Courtesy of the US Joint Global Ocean Flux Study

Their results predict a mean global carbon export flux of 6 petagrams (Pg) per year. Also known as a gigaton, a petagram is equal to one quadrillion (1015) grams.

This is a huge amount, roughly equivalent to the annual global emissions of fossil fuel. At present, fossil fuel combustion represents a flux to the atmosphere of approximately 9 Pg per year.

Ed note: To convert their scientist “C or carbon” lingo into CO2 just multiply their numbers by 3.67.



Global mean determinations of the efficiency of the biological pump from (left) the present food-web model and (right) an empirical method that models export efficiency as a function of the sea surface temperature (SST). Credit: UCSB

“It matters how big and small the plankton are, and it matters what the energy flows are in the food web,” Siegel said. “This is so simple. It’s really who eats whom but also having an idea of the biomasses and productivity of each.

So we worked out these advanced ways of determining NPP, phytoplankton biomass and the size structure to formulate mass budgets, all derived from satellite data.”

The researchers are hoping to take their model one step further by planning a major field program designed to better understand the states in which the biological pump operates. “Understanding the biological pump is critical,” Siegel concluded. “We need to understand where carbon goes, how much of it goes into the organic matter, how that affects the air-sea exchanges of CO2 and what happens to fossil fuel we have emitted from our tailpipes.”

Perhaps the most important information that is missing in this paper is the historical context of how the oceans are doing. Not well. It’s widely reported that ocean NPP is down globally by 40%. That represents an enormous loss of carbon uptake by the oceans. If the oceans were to come back to the level of productivity that they were in a century ago and that 40% loss were restored then ocean carbon uptake would be not taking in merely 6 gigatonnes C per year but rather 8.4 gigatonnes! In terms of CO2 that extra uptake if the oceans come back to life is 2.4X3.67= 8.8 gigatonnes of extra CO2  uptake per year. Therein lies the potential for repurposing CO2 in the ocean from its harmful form into ocean life.

 Portions of this post were originally published in Global Biogeochemical Cycles. Source: University of California – Santa Barbara