Ocean carbon in atomic detail


Rebecca Pool

Wednesday, June 6, 2018 - 06:30
Image: Ocean carbon imaged on the atomic scale [IBM Research]
IBM researchers and a team of oceanographers have unveiled the first images of the structure of dissolved ocean carbon, in a bid to understand how the world's massive carbon pool could respond to global warming.
Using atomic force microscopy, Leo Gross from IBM Zurich, and colleagues from the University of Zurich, University of California Irvine and University of California Santa Cruz, imaged the molecules from dissolved organic carbon taken from the ocean surface and deep waters of the North Pacific.
From left to right, Leo Gross, IBM Research Zurich; Alysha Inez Coppola, University of Zurich; Fabian Schulz, IBM Research Zurich and Shadi Fatayer, IBM Research Zurich.
Atomic resolution detail reveals significant differences between these molecules and represents a key step towards understanding the ocean-carbon cycle and long-term stability of the world's dissolved ocean carbon.
While the fate of most biomolecules and dissolved organic matter in the deep ocean is remineralisation to carbon dioxide which eventually escapes at the sea surface, some fixed carbon is instead stored for millennia as recalcitrant organic matter.
The processes and mechanisms involved in the generation of this huge carbon reservoir are poorly understood, but one key theory suggests that the long persistance of the deep ocean carbon is down to its chemical structure. 
With this in mind, Gross and colleagues turned to AFM to image individual molecules of dissolved carbon samples.
Using AFM with a carbon monoxide functionalised tip, the researchers discovered that molecules from the deep waters are more planar and feature fewer aliphatic groups than molecules from the ocean surface.
Left: AFM image using a CO-functionalised tip of 5,6,8-trimethyl-2,3-dihydro-1H-cyclopenta[b]naphthalene, a molecule found in the deep ocean. Right: AFM image using a CO-functionalised tip of a molecule found in the deep North Pacific Ocean.
"Atomic force microscopy resolved planar structures with features similar to polycyclic aromatic compounds and carboxylic-rich alicyclic structures with less than five aromatic carbon rings," writes Gross in Geophysical Research Letters. "These compounds comprise 8% and 20% of the measurable molecules investigated in the surface and deep, respectively." 
The latest results support the hypotheses that the old age of deep ocean dissolved organic carbon relates to its structural recalcitrance, critical to understanding how the carbon cycle will change as the world warms.
Marine researchers can now use this AFM method to investigate individual chemical structures present in the ocean basins to uncover the 'health' of oceans around the world.
Research is published in Geophysical Research Letters.
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