Dissolved organic matter dynamics in a whale-dominated coastal system: Insights from Península Valdés, Argentina

Dissolved organic matter (DOM) is increasingly being recognized as critical components of the global carbon cycle. Sheltered coastal areas that host high densities of large marine mammals may play a particularly important role in coastal carbon fluxes, but spatial and temporal changes in dissolved organic carbon (DOC) and nitrogen (DON) dynamics in coastal ecosystems remain largely unexplored. Here, we provide the first quantitative data on DOC and DON dynamics and sources in Golfo Nuevo, a protected gulf in the Península Valdés (Argentina) known as one of the most important calving grounds for the southwestern Atlantic population of the southern right whale (Eubalaena australis). Specifically, we show that Golfo Nuevo is a highly productive system that acts as a major source of DOM to the South Atlantic shelf. We also found that DOC and DON concentrations increased by 1.37- and 1.41-fold, respectively, during the whale calving season. The δ¹³C isotopic signal of this DOC indicated that it was predominantly whale- and phytoplankton-derived, suggesting a potential 'whale pump'. In addition, microbial carbon overconsumption during the whale calving season increased the DOC:DON ratio, indicating increased DOC refractoriness. Bioavailable DOC accounted for 18.6 %-52.7 % of the DOC pool, whereas the average recalcitrant DOC concentrations were 200 ± 19 μM and 180 ± 7 μM in the non-whale and whale seasons, respectively. Overall, our results highlight how large marine mammals can act as a vector for both, labile and recalcitrant DOC and thereby modulate DOM dynamics in coastal habitats.