Methanol Concentrations and Biological Methanol Consumption in the Northwest Pacific Ocean.

Methanol metabolism can play an important role in marine carbon cycling. We made contemporaneous measurements of methanol concentration and consumption rates in the northwest Pacific Ocean to constrain the pathways and dynamics of methanol cycling. Methanol was detected in relatively low concentrations (<12–391 nM), likely due to rapid biological turnover. Rates of methanol oxidation to CO2 (0.9–130.5 nmol L−1 day−1) were much higher than those of assimilation into biomass (0.09–6.8 nmol L−1 day−1), suggesting that >89.7% of methanol was utilized as an energy source. Surface water acted as a net methanol sink at most sites, with an average flux of 9 μmol L−1 day−1. Atmospheric deposition accounted for 22.7% of microbial methanol consumption in the mixed layer, illustrating that the atmosphere is less important than internal processes for driving methanol cycling in these pelagic waters. Plain Language Summary: Methanol is one of the most abundant oxygenated volatile organic compounds in the atmosphere and microbial methanol metabolism is an important part of the marine carbon cycle. However, only a limited number of studies describe methanol cycling in marine waters, and the sources and sinks of methanol remain largely unconstrained in the Pacific Ocean. We investigated the distribution and microbial consumption of methanol in the Kuroshio‐Oyashio extension region of northwest Pacific Ocean. Methanol was used primarily as an energy source and the rapid biological turnover of methanol contributed to relatively low‐standing stocks of methanol. Air‐sea flux estimates suggested that the atmosphere was a net source of methanol to the study area. Compared to in situ production and consumption rates, air‐sea exchange represented a less important process for methanol cycling in the mixed layer. Our results add to the global database of methanol concentrations and help to constrain the biological sources and sinks of methanol in the surface ocean. Key Points: Methanol was detected in relatively low concentrations due to rapid biological consumption in the Kuroshio‐Oyashio extension regionMuch higher oxidation rates than assimilation rates suggested methanol was predominantly used as an energy sourceAtmospheric deposition is a source of methanol in the mixed layer and accounted for 22.7% of microbial methanol consumption [ABSTRACT FROM AUTHOR]