Ocean Organic Carbon Persists For Millenia

Ocean Organic Carbon Persists For Millenia

European scientists working as part of the globally comprehensive Malaspina Expedition have shown deep ocean carbon is not promptly exhaled as CO2 by microbial activity but instead persists for thousands of years.

New understanding of ocean standing biomass

The new research has made major strides in the understanding of the mechanisms governing the persistence of dissolved organic carbon (DOC) for hundreds to thousands of years in the deep ocean. As the detritus of surface ocean plankton sinks into the deep on its way to the bottom some of it breaks up and dissolves becoming molecular organic carbon in the ocean water constantly refilling the vast pool of DOC. Much of that DOC which is found below the deep thermocline 500-1,000 meters down, the new report now shows, is not degraded by bacteria but instead remains stable and intact in countless chemical forms.



Until now, it was thought that the much carbon in the ocean abyss water column consisted of a number of non-degradable inorganic chemical compounds (DIC – dissolved inorganic carbon), but this study shows that abyssmal dissolved organic carbon DOC is also made up of thousands of readily degradable organic carbon compounds that are simply NOT degrading further. Think of this non-degrading biocarbon as the “biochar” of ocean pastures. The finding, published in the latest issue of the Science journal, provides new keys to better understand and quantify the enormous role of the ocean carbon cycle and the global climate.

Ocean Carbon Context

The ocean captures an enormous amount of carbon each year (~58 billion tonnes of CO2). Like a forest on land this sustains the oceans standing biomass that mostly resides in the surface ocean. While much of that standing ocean biomass carbon is consumed and re-exhaled as CO2 a very large amount is retained. A vastly larger amount some 40,000 billion tonnes CO2e, the product of millenia of accumulation in the form of dissolved organic and inorganic carbon resides in the entire volume of the worlds oceans. More has sunk all the way to the bottom and is in the process of being reincorporated into the earths geologic cycle. The atmosphere at ~400ppm CO2 by comparison contains about 3,000 billion tonnes of CO2. Our more familiar terra firma environs including all of terrestrial forests, vegetation, and soil carbon are reported to contain a mere 2,000 billion tonnes, 1/20th that in the oceans.

The oceans carbon system is driven by the same power of photosynthesis as the land covers about 2/3 of this blue planet manages 20 times more carbon than the land where plants can live on only 17% of the planet. So the real world of photosynthesis and carbon on this blue planet is clearly the oceans.

Malespina Expedition Chart

Malespina Expedition Chart – click to enlarge

The circumnavigation of the worlds oceans, performed by the Spanish research ship Hesperides was part of the Malaspina project and proved to be a unique opportunity to obtain an extensive sample and data collection from the Atlantic and Pacific oceans. For this study, scientists have used samples of dissolved organic material from the deep ocean obtained at different depths between 1,000 and 4,000 meters.

Until now, it was thought that this dissolved organic material in the deep ocean and believed to be mysteriously persistent was resistant to common microbial degradation but no explanation had become accepted. This lack of explanation led to persistent debate about the amount of DOC in the ocean. According to this new study bacteria simply can not cope with the thousands of different molecules that make up the deep carbon as those different molecules are found in individually very low concentrations. The expenditure of energy by bacteria adapt to and make use each of these molecules is prevented or greatly slowed by the low concentrations.

CSIC researchers concentrated the different molecules and tested their bioavailability to common microbial action: “By offering concentrated organic material from the deep water to bacteria, we have observed a stimulation of growth at higher concentrations, i.e., this organic material from the deep ocean, hitherto considered to be little or not degradable at all, is actually readily degradable for the deep-ocean microorganisms. The reason is that this large amount of organic carbon is a mixture of “leftovers” from easily degradable materials, but their use is limited by the existing low concentrations of each compound.”

Ocean Carbon Crisis

There is a crisis in the world of ocean carbon as ocean primary productivity is in cataclysmic decline around the world. Once lush ocean pastures full of life are now seen turning into blue deserts. The crisis of the ocean pastures is brought about by the high and rising CO2 in the world’s atmosphere. This high CO2 is destroying ocean pasture productivity by two mechanisms. First the high and rising CO2 in the air is good for plants on land and is producing a dramatic global greening. But more grass growing means less dust blowing and that dust in the wind is the most vital nutrient of all for ocean pastures. Dust is the Ying for the oceans just as rain is the Yang for the land.

There is hope for the oceans if humanity decides to practice being a good shepherd to its ocean pastures just as it learned to do thousands of years ago with its pastures on land.