Bacterial response to dust pulses in the western Mediterranean: Implications for carbon cycling in the oligotrophic ocean

[1] The bacterial response to dust pulses was investigated in the Mediterranean Sea through a combined field and experimental study. During the stratification period, characterized by a nutrient-starved mixed layer isolated from the depth, a Saharan dust event (2.6 gm(-2)) induced a 1.5-fold increase in bacterial abundance (BA) and a 2-fold increase in bacterial respiration (BR). Experimental dust additions (equivalent to fluxes of 5 and 20 g m(-2)) to bacteria natural assemblages also stimulated BA (between 2- and 4-fold increases) and BR (between 1.5- and 3-fold increases). Pooling the in situ and experimental data, linear relationships were obtained between dust concentration and BA (r(2) = 0.86; p < 0.01) and BR (r(2) = 0.89; p < 0.001). The dust-induced bacterial bloom resulted in a C mineralization of 0.5 g m(-2), which may represent up to 70% of bioavailable DOC annually exported to the depth in the Mediterranean. These results demonstrate that heterotrophic bacteria may play a much larger role in the connections between dust and the ocean carbon cycle than previously recognized and highlight the need for a more accurate understanding of how dust pulses may affect C export in the oligotrophic ocean.