Abstract. Oceanic emissions of the climate-relevant trace gases
carbonyl sulfide (OCS) and carbon disulfide (CS2) are a major source to
their atmospheric budget. Their current and future emission estimates are
still uncertain due to incomplete process understanding and therefore
inexact quantification across different biogeochemical regimes. Here we
present the first concurrent measurements of both gases together with
related fractions of the dissolved organic matter (DOM) pool, i.e.,
solid-phase extractable dissolved organic sulfur (DOSSPE, n=24,
0.16±0.04 µmol L−1), chromophoric (CDOM, n=76,
0.152±0.03), and fluorescent dissolved organic matter (FDOM, n=35),
from the Peruvian upwelling region (Guayaquil, Ecuador to Antofagasta,
Chile, October 2015). OCS was measured continuously with an equilibrator
connected to an off-axis integrated cavity output spectrometer at the
surface (29.8±19.8 pmol L−1) and at four profiles ranging down
to 136 m. CS2 was measured at the surface (n=143, 17.8±9.0 pmol L−1) and below, ranging down to 1000 m (24 profiles). These
observations were used to estimate in situ production rates and identify their
drivers. We find different limiting factors of marine photoproduction: while
OCS production is limited by the humic-like DOM fraction that can act as a
photosensitizer, high CS2 production coincides with high DOSSPE
concentration. Quantifying OCS photoproduction using a specific humic-like
FDOM component as proxy, together with an updated parameterization for dark
production, improves agreement with observations in a 1-D biogeochemical
model. Our results will help to better predict oceanic concentrations and
emissions of both gases on regional and, potentially, global scales.
Understanding and modelling fluorescent dissolved organic matter probe readings for improved coagulation performance in water treatment plants
