Citation:

fmars.2017.00024

Name: Nitrous oxide and biogeochemical variables related to Intermediate Waters into Eastern South Pacific Ocean
Published: 2019-09-23
License: https://creativecommons.org/licenses/by/4.0/
Keywords: Greenhouse gases; nitrate; nitrite; nitrogen cycle; nitrous oxide; oceanography; Salinity; silicate; Temperature

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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 10º and 60°S, and ~75° to 88°W, from intermediate waters targeting Antarctic Intermediate Water (AAIW) at potential density of 27.0-27.1 kg m-3. Between 60° to 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 (∆N2O) and O2 utilization (AOU), and between ∆N2O and NO3-, 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 ∆N2O vs. NO3- and ∆N2O vs. N* (a Nitrogen deficit index) and because ∆N2O 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.

Keyword(s):

Greenhouse gases; nitrate; nitrite; nitrogen cycle; nitrous oxide; oceanography; Salinity; silicate; Temperature

Coverage:

Median Latitude: -31.152414 * Median Longitude: -76.273946 * South-bound Latitude: -60.167000 * West-bound Longitude: -91.407000 * North-bound Latitude: -9.496000 * East-bound Longitude: -70.755000

Date/Time Start: 2003-10-06T00:00:00 * Date/Time End: 2010-12-01T00:00:00

Minimum DEPTH, water: 1 m * Maximum DEPTH, water: 2000 m

Event(s):

BiG_RAPA-1 * Latitude: -20.084000 * Longitude: -70.800000 * Date/Time: 2010-11-20T00:00:00 * Campaign: (Biogeochemical Gradients: Role in Arranging Planktonic Assemblages) * Basis: Melville * Method/Device: (CTD-RO)

BiG_RAPA-2 * Latitude: -21.178000 * Longitude: -76.573000 * Date/Time: 2010-11-26T00:00:00 * Campaign: (Biogeochemical Gradients: Role in Arranging Planktonic Assemblages) * Basis: Melville * Method/Device: (CTD-RO)

BiG_RAPA-3 * Latitude: -22.261000 * Longitude: -82.348000 * Date/Time: 2010-11-27T00:00:00 * Campaign: (Biogeochemical Gradients: Role in Arranging Planktonic Assemblages) * Basis: Melville * Method/Device: (CTD-RO)

Comment:

Seven oceanographic cruises which include the vertical distribution of Nitrous Oxide, Oxygen, Silicate, Nitrate, Nitrite, Phosphate, Temperature, Salinity and estimated variable such as Density and Potential Density, are shared. The cruises cover the South Eastern Pacific Ocean between -9.5 to -60 °S and -70.7 to -91.4 °W and from surface up 2000 meters depth. Nitrous Oxide was analyzed in 20 ml vials with headspace by Gas Chromatography, while the Temperature, Salinity, Pressure and Dissolved Oxygen were determinate using a calibrated CTD-O probe. Nutrients were filtered with 0.45 micras pore size glass filter and determine by colorimetry.

Water samples were collected using Niskin bottles attached to rosette sampler, in order to obtain discrete measurements of dissolver oxygen (O2) and nutrients (NO3, NO2, SiO4 and PO43). Discrete samples of DO (in triplicate) were analyzed using the AULOX measurement system, an automatic Winkler method. Samples for all nutrients (15 mL in triplicate) were filtered (using a 0.45 μm GF/F glass filter) and stored (frozen) until analysis, using standard colorimetric techniques (Grasshoff, 1983). N2O samples were taken in triplicate in 20 mL vials and carefully sealed to avoid air bubbles. They were then preserved with 50 μL of saturated HgCl2 and stored in darkness until analysis. N2O was analyzed by creating a 5 mL headspace of ultrapure Helium (He) and then equilibrated within the vial, and measured by gas chromatography (Shimadzu 17A) using an electron capture detector (ECD). The calibration curves were made previous to each measurement with five points using pure He, 0.1, 0.5, and 1 of N2O standards and dry air. The ECD detector linearly responded to this concentration range and the analytical error for N2O measurements was ~3%. The uncertainty of the measurements was calculated from the standard deviation of the triplicate measurements by depth. Samples with a variation coefficient above 10% were not considered in the N2O database.

Parameter(s):

#	Name	Short Name	Unit	Principal Investigator	Method/Device	Comment
1	Event label	Event		Farías, Laura
2	Cruise/expedition	Expedition		Farías, Laura
3	Cruise/expedition	Expedition		Farías, Laura		R/V
4	Station label	Station		Farías, Laura		Station
5	Latitude of event	Latitude		Farías, Laura
6	Longitude of event	Longitude		Farías, Laura
7	DATE/TIME	Date/Time		Farías, Laura		Geocode
8	DEPTH, water	Depth water	m	Farías, Laura		Geocode
9	Temperature, water	Temp	°C	Farías, Laura	CTD-O probe
10	Salinity	Sal		Farías, Laura	CTD-O probe
11	Density, mass density	Density	kg/m³	Farías, Laura
12	Oxygen	O2	µmol/kg	Farías, Laura	CTD-O probe	Dissolved
13	Oxygen	O2	µmol/l	Farías, Laura	Dissolved oxygen, automated Winkler (Strickland & Parsons, 1972)	Dissolved
14	Nitrous oxide, dissolved	N2O	nmol/l	Farías, Laura	Headspace Gas Chromatography, Perkin-Elmer
15	Silicate	Si(OH)4	µmol/l	Farías, Laura	Seawater analysis after Grasshoff et al., 1983 (Verlag Chemie GmbH Weinheim)
16	Nitrate	[NO3]-	µmol/l	Farías, Laura	Seawater analysis after Grasshoff et al., 1983 (Verlag Chemie GmbH Weinheim)
17	Nitrite	[NO2]-	µmol/l	Farías, Laura	Seawater analysis after Grasshoff et al., 1983 (Verlag Chemie GmbH Weinheim)
18	Phosphate	[PO4]3-	µmol/l	Farías, Laura	Seawater analysis after Grasshoff et al., 1983 (Verlag Chemie GmbH Weinheim)
19	Density, mass density	Density	kg/m³	Farías, Laura		Potential Density

Change history:

2020-05-25T19:26:53 – Event labels for 2006 were updated and date/time added

License:

Creative Commons Attribution 4.0 International (CC-BY-4.0)

Size:

11930 data points

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