[EN638 LV Cell Counts] - Cell abundance in HMW-DOM amended mesocosm incubations from water collected in the Western North Atlantic during the research cruise EN638 in May 2019 aboard R/V Endeavor (A mechanistic microbial underpinning for the size-reactivity continuum of dissolved organic carbon degradation)

The existence of a size-reactivity continuum of DOM - observations and measurements showing that high molecular weight (HMW) DOM tends to be younger and more reactive than lower MW DOM - has been demonstrated in laboratory and field investigations in different parts of the ocean.

A mechanistic explanation for the greater reactivity of HMW DOM has been lacking, however. Here we investigated the potential of seawater microbial communities from different water masses and under differing conditions of organic matter availability to hydrolyze six high-molecular-weight polysaccharides (arabinogalactan, chondroitin sulfate, fucoidan, laminarin, pullulan, and xylan). Samples were taken from incubation experiments of DCM, OMZ, and bottom waters aboard R/V Endeavor (EN638), May 2019 in the Northern Atlantic.