Publication Date:
2019-07-16
Description:
Coastal upwelling ecosystems are areas of high productivity and strong outgassing, where most gases,
such as N2O and CH4, are produced in subsurface waters by anaerobic metabolisms. We describe seasonal
CH4 variation as well as potential mechanisms producing CH4 in surface waters of the central Chile
upwelling ecosystem (36°S). Surface waters were always supersaturated in CH4 (from 125% up to
550%), showing a clear seasonal signal triggered by wind driven upwelling processes (austral spring–
summer period), that matched with the periods of high chlorophyll-a and dimethylsulfoniopropionate
(DMSP) levels. Methane cycling experiments, with/without the addition of dimethylsulfide (including
13C-DMS) and acetylene (a nonspecific inhibitor of CH4 oxidation) along with monthly measurements
of CH4, DMSP and other oceanographic variables revealed that DMS can be a CH4 precursor. Net CH4
cycling rates (control) fluctuated between -0.64 and 1.44 nmol L-1 d-1. After the addition of acetylene,
CH4 cycling rates almost duplicated relative to the control, suggesting a strong methanotrophic activity.
With a spike of DMS, the net CH4 cycling rate significantly increased relative to the acetylene and control
treatment. Additionally, the d13C values of CH4 at the end of the incubations (after addition of 13C
enriched-DMS) were changed, reaching -32‰ PDB compared to natural values between -44‰ and
-46‰ PDB. These findings indicate that, in spite of the strong CH4 consumption by methanotrophs, this
upwelling area is an important source of CH4 to the atmosphere. The effluxes are derived partially from
in situ surface production and seem to be related to DMSP/DMS metabolism.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf
