Oral communicationDissolved organic matter (DOM) plays a major role in the recycling,
export and sequestration of biogenic organic carbon, being a key
component of ocean biogeochemical cycles and of the biological and
microbial carbon pumps. Microbial degradation of DOM not only
produces CO 2 but also generates dissolved molecules of decreasing
bioavailability that can accumulate in the oceans for hundreds to
thousands of years. The size-reactivity continuum (SRC) model is the
conceptual framework to explain the DOM reactivity on a size basis,
although field tests are still scarce and some of the pieces of this
puzzle remain unclear. Taking advantage of the FLUXES-I cruise in the
Cape Verde Frontal Zone (CVFZ), we have studied the size fractionated reactivity of the high (HMW; >1 KDa) and low (LMW; <1
KDa) molecular weight fractions of the DOM from surface down to
4000 m, using a high-efficiency and low-concentration-factor
ultrafiltration cell. The wide ageing range covered by the water
masses of the CVFZ makes it an excellent site to test the SRC model.
Regarding the bulk C and N pools, the water masses with higher
oxygen utilization were more depleted in HMW molecules, with a
significant preference for the degradation of large N-containing
compounds. Accordingly, preferential degradation of HMW
fluorescent protein-like compounds was observed. In parallel,
fluorescent humic-like compounds of both HMW and LMW were
generated as by-product of the degradation of HMW organic
compounds, and the remineralization of the DOM increases the
aromaticy of both fractions, but especially the LMW one.ASL
