In:
Biogeosciences, Copernicus GmbH, Vol. 16, No. 9 ( 2019-05-17), p. 2079-2093
Abstract:
Abstract. The open ocean is a major source of nitrous oxide
(N2O), an atmospheric trace gas attributable to global warming and
ozone depletion. Intense sea-to-air N2O fluxes occur in major oceanic
upwelling regions such as the eastern tropical South Pacific (ETSP). The
ETSP is influenced by the El Niño–Southern Oscillation that leads to
inter-annual variations in physical, chemical, and biological properties in
the water column. In October 2015, a strong El Niño event was developing
in the ETSP; we conduct field observations to investigate (1) the N2O
production pathways and associated biogeochemical properties and (2) the
effects of El Niño on water column N2O distributions and fluxes
using data from previous non-El Niño years. Analysis of N2O natural
abundance isotopomers suggested that nitrification and partial
denitrification (nitrate and nitrite reduction to N2O) were occurring
in the near-surface waters; indicating that both pathways contributed to
N2O effluxes. Higher-than-normal sea surface temperatures were
associated with a deepening of the oxycline and the oxygen minimum layer.
Within the shelf region, surface N2O supersaturation was nearly an
order of magnitude lower than that of non-El Niño years. Therefore, a
significant reduction of N2O efflux (75 %–95 %) in the ETSP
occurred during the 2015 El Niño. At both offshore and coastal stations,
the N2O concentration profiles during El Niño showed moderate
N2O concentration gradients, and the peak N2O concentrations
occurred at deeper depths during El Niño years; this was likely the
result of suppressed upwelling retaining N2O in subsurface waters. At
multiple stations, water-column inventories of N2O within the top 1000 m were up to 160 % higher than those measured in non-El Niño years,
indicating that subsurface N2O during El Niño could be a reservoir
for intense N2O effluxes when normal upwelling is resumed after El
Niño.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-16-2079-2019
DOI:
10.5194/bg-16-2079-2019-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2158181-2
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