The vast reservoir of carbon that is stored in soils probably is more sensitive to destabilization from climate change than has previously been assumed, according to a new study by researchers at WHOI and other institutions.
The study found that the biospheric carbon turnover within river basins is vulnerable to future temperature and precipitation perturbations from a changing climate.
Although many earlier, and fairly localized, studies have hinted at soil organic carbon sensitivity to climate change, the new research sampled 36 rivers from around the globe and provides evidence of sensitivity at a global scale.
"The study results indicate that at the large ecosystem scale of river basins, soil carbon is sensitive to climate variability," said WHOI researcher Timothy Eglinton, co-lead author of the paper in the Proceedings of the National Academy of Sciences of the United States of America. "This means that changing climate, and particularly increasing temperature and an invigorated hydrological cycle, may have a positive feedback in terms of returning carbon to the atmosphere from previously stabilized pools of carbon in soils."
The public is generally aware that climate change can potentially destabilize and release permafrost carbon into the atmosphere and exacerbate global warming. But the study shows that this is true for the entire soil carbon reservoir, said WHOI researcher Valier Galy, the other co-lead author of the study.
The soil carbon reservoir is a key component in keeping the atmosphere in check in terms of how much carbon dioxide is in the air. The amount of carbon stored in terrestrial vegetation and soils is three times more than how much the atmosphere holds, and it consumes more than a third of the anthropogenic carbon that is emitted to the atmosphere.
To determine the sensitivity of terrestrial carbon to destabilization from climate change, researchers measured the radiocarbon age of some specific organic compounds from the mouths of a diverse set of rivers. Those rivers--including the Amazon, Ganges, Yangtze, Congo, Danube, and Mississippi--account for a large fraction of the global discharge of water, sediments and carbon from rivers to the oceans.
Terrestrial carbon, however, is not so simple to isolate and measure. That's because carbon in rivers comes from a variety of sources, including rocks, organic contaminants such as domestic sewage or petroleum that differ widely in their age, and vegetation. To determine what's happening within the rivers' watersheds, and to measure radiocarbon from the terrestrial biosphere, researchers focused on two groups of compounds: the waxes of plant leaves that serve a protective function for the plants' leaf surface and lignin, which is the woody "scaffolding" of land plants.
Taking these measurements showed a relationship between the age of the terrestrial carbon in the rivers and the latitude where the rivers reside, researchers found. That latitudinal relationship prompted researchers to infer that climate must be a key control in the age of the carbon that is exported from the terrestrial biosphere to these rivers, and that temperature and precipitation are primary controls on the age of that carbon.
"Why this study is powerful is because this large number of rivers, the wide coverage, and the wide range of catchment properties give a very clear picture of what's happening at the global scale," said Galy. "You could imagine that by going after lots of rivers, we would have ended up with a very complicated story. However, as we kept adding new river systems to the study, the story was fairly consistent."
"In many respects, Earth scientists see rivers as being a source signal that is sent to sedimentary records that we can interpret," said Eglinton. "By going to sedimentary records, we have the opportunity to look at how the terrestrial biosphere has responded to climate variability in the past. In addition, by monitoring rivers in the present day, we can also use them as sentinels in order to assess how these watersheds may be changing."
About Woods Hole Oceanographic Institution
The Woods Hole Oceanographic Institution (WHOI) is a private, non-profit organization on Cape Cod, Massachusetts, dedicated to marine research, engineering, and higher education. Established in 1930, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate an understanding of the ocean's role in the changing global environment. WHOI's pioneering discoveries stem from an ideal combination of science and engineering--one that has made it one of the most trusted and technically advanced leaders in basic and applied ocean research and exploration anywhere. WHOI is known for its multidisciplinary approach, superior ship operations, and unparalleled deep-sea robotics capabilities. We play a leading role in ocean observation and operate the most extensive suite of data-gathering platforms in the world. Top scientists, engineers, and students collaborate on more than 800 concurrent projects worldwide--both above and below the waves--pushing the boundaries of knowledge and possibility. For more information, please visit http://www.whoi.edu
Additional authors and institutions:
Timothy I. Eglinton: a,b,1
Valier V. Galy: b,1
Jordon D. Hemingway: b,c
Xiaojuan Feng: a,b,d
Hongyan Bao: e,3
Thomas M. Blattmann: a,4
Angela F. Dickens: b,5
Hannah Gies: a
Liviu Giosan: f
Negar Haghipour: a,g
Pengfei Hou: h
Maarten Lupker: a
Cameron P. McIntyre: a,g,6
Daniel B. Montluçon: a
Bernhard Peucker-Ehrenbrink: b
Camilo Ponton: f,7
Enno Schefuß: b,i,
Melissa S. Schwab: a
Britta M. Voss: b,8
Lukas Wacker: g
Ying Wu: e
a: Department of Earth Sciences, ETH Zurich, 8092, Switzerland
b: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543
c: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
d: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
e: State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China
f: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543
g: Laboratory for Ion Beam Physics, Department of Physics, ETH Zurich, 8093 Zurich, Switzerland
h: Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University China, Qingdao 266100, China
i: Center for Marine Environmental Sciences, University of Bremen, Bremen 28359, Germany
1: T.I.E. and V.V.G. contributed equally to this work
Proceedings of the National Academy of Sciences