Concentrations and Reactivities of Refractory Carboxyl-rich Alicyclic Molecules (CRAM) in Contrasting Natural Waters

The production of refractory dissolved organic matter (RDOM) by microbes represents an important mechanism of carbon sequestration in the deep ocean (i.e., the microbial carbon pump). Despite recent progress, our quantitative understanding of the microbial carbon pump remains impeded by our limited knowledge of the complex chemical composition of RDOM and of the specific cycling of its constituents. Carboxyl-rich alicyclic molecules (CRAM) have been identified as an abundant class of refractory organic molecules and have been observed both in the deep ocean and in freshwater. Although these observations suggest that CRAM could be ubiquitous in natural waters, the actual variability of CRAM concentrations in natural waters and their susceptibility to microbial and photochemical degradation remain largely unknown. Here, we report CRAM concentrations measured by NMR from a set of contrasting natural waters collected around the world (e.g., boreal river and estuary, coastal upwelling region, coastal marsh, open ocean) in an effort to better understand its distribution and potential sources. Photochemical and microbial experiments were also carried out on the samples in order to evaluate the microbial and photochemical reactivities of CRAM from these contrasting waters. A better understanding of the sources and cycling of identified components of RDOM like CRAM can provide valuable insights into our understanding of the microbial carbon pump.