Occurrence and emissions of biogenic dimethylated sulfur compounds and their responses to mesoscale eddies and typhoon Yutu in the western tropical Pacific Ocean

Abstract

The western tropical Pacific Ocean (WTPO) plays a vital role in the global sulfur biogeochemical cycle. Here, an investigation was conducted to explore the spatial variations in biogenic dimethylated sulfur compounds (BDSCs) and their controlling factors in the WTPO in 2018. Dimethylsulfide (DMS) sea-to-air fluxes and the contribution of DMS emissions to the atmospheric sulfate burden were estimated. The concentrations of BDSCs in the surface seawater were low compared to the marginal seas of the western Pacific Ocean, attributed to a limited supply of nutrients and low primary production. Besides, higher values of the BDSCs were observed in surface and subsurface water. The nanophytoplankton was the main dimethylsulfoniopropionate (DMSP) producer, and the abundance of low DMSP and dimethylsulfoxide (DMSO) producers determined the DMSP/O concentrations in the oligotrophic WTPO. Moreover, mixed layer depth might be the crucial factor affecting DMS values. DMS fluxes were low in the WTPO, but they still contributed substantially to global DMS emissions, given the vast areas of the Pacific Ocean. The contribution of biogenic non-sea-salt sulfate (nss-SO₄^2-) to total SO₄^2- reached 25.87%, which showed the oxidation products of DMS were the crucial sources of SO₄^2- in aerosols. Responses of BDSCs to mesoscale eddies and a typhoon were investigated for the first time. The warm eddy increased the concentrations of chlorophyll a (Chl-a) and BDSCs. Nevertheless, no effect of a mesoscale cold eddy on Chl-a or BDSCs was evident. The values of Chl-a, DMS, DMSP, biogenic nss-SO₄^2-, and the DMS fluxes increased after Typhoon Yutu passed, indicating that typhoons play a prominent role in DMS emissions and the global sulfur cycles.