Journal
ENVIRONMENTAL RESEARCH LETTERS
Volume 10, Issue 4, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1748-9326/10/4/044017
Keywords
nitrous oxide hotspot; seasonal and inter-annual N2O variability; coastal upwelling; central Chile
Funding
- Fondo Nacional de Desarrollo Cientifico y Tecnologico (FONDECYT) [1090446]
- Fondo de Financiamiento de Centros de Investigacion en Areas Prioritarias (FONDAP) [1511009]
- ICM project (IMO) [120019]
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Seasonal and inter-annual variabilities of biogeochemical variables, including nitrous oxide (N2O), an important climate active gas, were analyzed during monthly observations between 2002 and 2012 at an ocean Time-Series station in the coastal upwelling area off central Chile (36 degrees 30.8'; 73 degrees 15'). Oxygen, N2O, nutrients and chlorophyll-a (Chl-a) showed clear seasonal variability associated with upwelling favorable winds (spring-summer) and also inter-annual variability, which in the case of N2O was clearly observed during the occurrence of N2O hotspots with saturation levels of up to 4849%. These hotspots consistently took place during the upwelling-favorable periods in 2004, 2006, 2008, 2010 and 2011, below the mixed layer (15-50 m depth) in waters with hypoxia and some NO2- accumulation. The N2O hotspots displayed excesses of N2O (Delta N2O) three times higher than the average monthly anomalies (2002-2012). Estimated relationships of Delta N2O versus apparent oxygen utilization (AOU), and Delta N2O versus NO3-, suggest that aerobic ammonium oxidation (AAO) and partial denitrification are the processes responsible for high N2O accumulation in subsurface water. Chl-a levels were reasonably correlated with the presence of the N2O hotspots, suggesting that microbial activities fuelled by high availability of organic matters lead to high N2O production. As a result, this causes a substantial N2O efflux into the atmosphere of up to 260 mu mol m(-2) d(-1). The N2O hotspots are transient events or hot moments, which may occur more frequently than they are observed. If so, this upwelling area is producing and emitting greater than expected amounts of N2O and is therefore an important N2O source that should be considered in the global atmospheric N2O balance.
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