Isoprene Production and Its Driving Factors in the Northwest Pacific Ocean

Marine isoprene plays a crucial role in the formation of secondary organic aerosol within the remote marine boundary layer. Due to scarce field measurements of oceanic isoprene and limited laboratory-based studies of isoprene production, assessing the importance of marine isoprene on atmospheric chemistry and climate is challenging. Calculating in-field isoprene production rates is a crucial step to predict marine isoprene concentrations and the subsequent emissions to the atmosphere. The distribution, sources, and dominant environmental factors of isoprene were determined in the Northwest Pacific Ocean in 2019. The nutrient enrichment in the Kuroshio Oyashio Extension (KOE) surface seawater, driven by the upwelling and atmospheric deposition, promoted the growth of phytoplankton and elevated the isoprene concentration. This was confirmed by observed responses of isoprene to nutrients and aerosol dust additions in a ship-based incubation experiment, where the isoprene concentrations increased by 70% (t = 4.417, p < 0.001) and 35% (t = 2.387, p < 0.05), respectively. Biogenic isoprene production rates in the deck incubation experiments were positively related to chlorophyll a, temperature, and solar radiation, with an average production of 7.33 ± 4.27 pmol L⁻¹ day⁻¹. Photochemical degradation of dissolved organic matter was likely an abiotic source of isoprene, contributing to approximately 14% of the total production. Driven by high isoprene production and extreme physical disturbance, the KOE showed very high emissions of isoprene of 46.0 ± 13.0 nmol m⁻² day⁻¹, which led to a significant influence on the oxidative capacity of the local atmosphere.