Determination of apparent quantum yield spectra of DMS photo‐degradation in an in situ iron‐induced Northeast Pacific Ocean bloom

The wavelength dependence of the photochemical removal efficiency for DMS was studied for samples from an iron‐induced bloom in the Northeastern Pacific Ocean. In July 2002, a 64 km 2 patch of ocean was iron‐fertilized near Ocean Station Papa (50°12′N; 144°45′W). Only small changes in pseudo‐first‐order apparent quantum yield (AQY* DMS (λ)) were observed outside the iron‐patch. However, inside the patch, AQY* DMS (λ) decreased considerably over the two weeks following the initial iron injection. A positive strong correlation was found between pseudo‐first‐order apparent quantum yield determined at 330 nm (AQY* DMS (330 nm)) and NO 3 − concentrations. We propose that NO 3 − ‐photolysis has a substantial influence on DMS photo‐degradation rates in oceanic waters. This finding demonstrates that in addition to control DMS production, marine phytoplankton could indirectly influence the DMS photochemical loss rate via its control on NO 3 − distribution.