ABSTRACT: Large particles (60 µm) were collected using in situ pumps deployed at 30 and 200 m depth at 2 typical stations in the southern Indian Ocean (Polar Front Zone [PFZ] and Sub-Antarctic Area [SAr]). The samples were incubated in vitro with their own bacterial assemblages for 7 to 17 days in batches under oxic conditions in the dark. Particulate organic carbon (POC) and sugars were monitored over time. Particulate sugars (PCHO-C) accounted for 5 to 20% of POC in the SAr, while they represented 5 to 8% of POC in the PFZ station at the beginning of the experiments. Molecular level analysis indicated that at the time of collection, ribose was among the most abundant sugars (18 to 30 wt% of PCHO-C) at the PFZ station and was rapidly degraded (k = 0.051 to 0.058 d–1) over the course of the experiment, while this sugar was below detection limits in the SAr. Our results also showed an increase in the relative abundance of deoxysugars (fucose and rhamnose), suggesting that these sugars have the potential to be used as indicators of the bacterial activity and evaluate the degradation status of POM in both areas. The kinetic study indicated that pentoses were degraded faster than hexoses, while deoxysugars exhibited the lowest degradation rates. This study demonstrated that total sugar degradation rates do not reflect the rates of all individual components, but rather a disparate collection of rates among sugars classes and individual sugars, which very likely can vary significantly in relation to the origin of particles.
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