On the Nitrous Oxide Accumulation in Intermediate Waters of the Eastern South Pacific Ocean.

Carrasco, Cristina, Karstensen, Johannes and Farias, Laura (2017) On the Nitrous Oxide Accumulation in Intermediate Waters of the Eastern South Pacific Ocean. Open Access Frontiers in Marine Science, 4 . Art.Nr. 24. DOI 10.3389/fmars.2017.00024.

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Abstract

Nitrous oxide (N2O) is a powerful greenhouse gas principally produced by nitrification and denitrification in the marine environment. Observations were made in the eastern South Pacific (ESP), between 10° and 60°S, and ~75°–88°W, from intermediate waters targeting Antarctic Intermediate Water (AAIW) at potential density of 27.0–27.1 kg m−3. Between 60° and 20°S, a gradual equatorward increase of N2O from 8 to 26 nmol L−1 was observed at density 27.0–27.1 kg m−3 where AAIW penetrates. Positive correlations were found between apparent N2O production (ΔN2O) and O2 utilization (AOU), and between ΔN2O and NO−3, which suggested that local N2O production is predominantly produced by nitrification. Closer to the equator, between 20° and 10°S at AAIW core, a strong N2O increase up to 75 nmol L−1 was observed. Because negative correlations were found between ΔN2O vs. NO−3 and ΔN2O vs. N* (a Nitrogen deficit index) and because ΔN2O and AOU do not follow a linear trend, we suspect that, in addition to nitrification, denitrification also takes place in N2O cycling. By making use of water mass mixing analyses, we show that an increase in N2O occurs in the region where high oxygen from AAIW merges with low oxygen from Equatorial Subsurface Water (ESSW), creating favorable conditions for local N2O production. We conclude that the non-linearity in the relationship between N2O and O2 is a result of mixing between two water masses with very different source characteristics, paired with the different time frames of nitrification and denitrification processes that impact water masses en route before they finally meet and mix in the ESP region.

Document Type: Article
Keywords: N2O; accumulation, nitrification, denitrification, eastern South Pacific Ocean, watermassanalysis, intermediate waters
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-PO Physical Oceanography
OceanRep > SFB 754
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.3389/fmars.2017.00024
ISSN: 2296-7745
Projects: SFB754, FONDAP
Expeditions/Models/Experiments:
Date Deposited: 24 Apr 2017 10:07
Last Modified: 01 Feb 2019 15:00
URI: http://oceanrep.geomar.de/id/eprint/37646

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