Evidence for non-selective preservation of organic matter in sinking marine particles

The sinking of particulate organic matter from ocean surface waters transpo rts carbon to the ocean interior(1,2), where almost all is then recycled. T he unrecycled fraction of this organic matter can become buried in ocean se diments, thus sequestering carbon and so influencing atmospheric carbon dio xide concentrations(3). The processes controlling the extensive biodegradat ion of sinking particles remain unclear, partly because of the difficulty i n resolving the composition of the residual organic matter at depth with ex isting chromatographic techniques(4). Here, using solid-state C-13 NMR spec troscopy(5), we characterize the chemical structure of organic carbon in bo th surface plankton and sinking particulate matter from the Pacific Ocean(4 ) and the Arabian Sea(6). We found that minimal changes occur in bulk organ ic composition, despite extensive (>98%) biodegradation, and that aminoacid -like material predominates throughout the water column in both regions. Th e compositional similarity between phytoplankton biomass and the small remn ant of organic matter reaching the ocean interior indicates that the format ion of unusual biochemicals, either by chemical recombination(7) or microbi al biosynthesis(8), is not the main process controlling the preservation of particulate organic carbon within the water column at these two sites. We suggest instead that organic matter might be protected from degradation by the inorganic matrix of sinking particles.