Dataset: OUTPACE - water column nitrate+nitrite

Name: Water column nitrate+nitrite d15N measurements from R/V L'Atalante in the southwest Pacific Ocean between New Caledonia and Tahiti from February to March 2015
Published: 2018-04-11
Keywords: nitrogen, Nitrate d15N, d15N budget, southwest Pacific, nitrogen fixation, oceans

Cite This Dataset

DOI:10.1575/1912/bco-dmo.733303

Spatial Extent: N:-18.179 E:-172.7813 S:-19.9832 W:168.0118

Temporal Extent: 2015-02-23 - 2015-03-30

Project:

Quantifying nitrogen fixation along unique geochemical gradients in the southwest Pacific Ocean (SW Pac N2 fixation)

Principal Investigator:

Angela N. Knapp (Florida State University, FSU)

International Collaborator:

Sophie Bonnet (Mediterranean Institute of Oceanography, MIO)

Thierry Moutin (Mediterranean Institute of Oceanography, MIO)

Scientist:

Oliver Grosso (Mediterranean Institute of Oceanography, MIO)

Nathalie Leblond (Villefranche Oceanographic Laboratory, LOV)

Student:

Kelly M. McCabe (Florida State University, FSU)

Contact:

Angela N. Knapp (Florida State University, FSU)

BCO-DMO Data Manager:

Mathew Biddle (Woods Hole Oceanographic Institution, WHOI BCO-DMO)

Version:

2018-04-11

Version Date:

2018-04-11

Restricted:

Validated:

Yes

Current State:

Final no updates expected

Water column nitrate+nitrite d15N measurements from R/V L'Atalante in the southwest Pacific Ocean between New Caledonia and Tahiti from February to March 2015

Abstract:

Constraining the rates and spatial distribution of di-nitrogen (N2) fixation fluxes to the ocean informs our understanding of the environmental sensitivities of N2 fixation as well as the timescale over which the fluxes of nitrogen (N) to and from the ocean may respond to each other. Here we quantify rates of N2 fixation as well as its contribution to export production along a zonal transect in the Western Tropical South Pacific (WTSP) Ocean using N isotope (“d15N”) budgets. Comparing measurements of water column nitrate+nitrite d15N with the d15N of sinking particulate N at a western, central, and eastern station, these d15N budgets indicate high, modest, and low rates of N2 fixation at the respective stations. The results also imply that N2 fixation supports exceptionally high, i.e., >50%, of export production at the western and central stations, which are also proximal to the largest iron sources. These geochemically-based rates of N2 fixation are equal to or greater than those previously reported in the tropical North Atlantic, indicating that the WTSP Ocean has the capacity to support globally significant rates of N2 fixation, which may compensate for N removal in the oxygen deficient zones of the eastern tropical Pacific.

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Archival Copy

Version Date	Archive	Persistent Identifier	Date Assigned
2018-04-11	Marine Biological Laboratory/Woods Hole Oceanographic Institution Library (MBLWHOI DLA)	10.1575/1912/bco-dmo.733303	2018-04-13

Description

This data set includes water column nitrate+nitrite d15N measurements. These measurements were used together with measurements of the d15N of particulate nitrogen collected in floating sediment traps that were deployed for several days to calculate the relative contribution of subsurface nitrate and nitrogen from N2 fixation for supporting export production (“d15N budgets”). The results suggest that N2 fixation supported a majority of export at Long Duration (LD) stations A and B, and a minor fraction of export at LD C. The results at LD stations A and B are unique compared to other d15N budgets from the oligotrophic regions, whereas the results from LD C are similar to prior reports from the eastern tropical South Pacific as well as the North Pacific near Hawaii. Additionally, these data are compared with other metrics of N2 fixation made on the same cruise.

Methods & Sampling

NO3-+NO2- d15N analysis was by the “denitrifier method” and followed the methods described by Sigman et al., 2001, Casciotti et al., 2002, McIlvin and Casciotti, 2011, and Weigand et al., 2016. Briefly, NO3-+NO2- was quantitatively reduced to N2O by Pseudomonas aureofaciens and Pseudomonas chlororaphis, which was then cryogenically focused and analyzed on an isotope ratio mass spectrometer. A volume of sample was added to each bacterial vial to achieve a final quantity of 10 or 20 nmols N2O, which was then purged from the vial using a helium carrier gas. The d15N of N2O in samples was calibrated with the international isotopic reference materials described in the Processing Description.

Data Processing Description

Nitrate+nitrite concentration was measured by others using colorimetric methods, and can be found at:
http://www.obs-vlfr.fr/proof/php/outpace/outpace.php

The average precision of nitrate+nitrite d15N measurements was <0.2 per mil, but with the standard deviation for duplicate analyses of each sample reported here. Samples were calibrated with IAEA N3 and USGS 34 NO3- d15N isotopic reference materials as described in McIlvin and Casciotti, 2011.

BCO-DMO Processing Notes:

added conventional header with dataset name, PI name, version date.
modified parameter names to conform with BCO-DMO naming conventions.
re-formatted date from dd Month yyyy (day month year) to yyyymmdd.
appended date, latitude, and longitude to each data entry.
If an observation did not exist, 'nd' (no data) was inserted.

Data Files

File
OUTPACE.csv (Comma Separated Values (.csv), 5.24 KB) MD5:2b45eb3c7b6fdb0b23e874a5726846d7 Primary data file for dataset ID 733237

More Information about this dataset

Funding Sources

Funding Source	Award Number
NSF Division of Ocean Sciences	OCE-1537314

Deployments

Deployment	Synonyms	Start Date	Platform	Investigator
OUTPACE		2015-02-18	R/V L'Atalante	Thierry Moutin (Chief Scientist) Sophie Bonnet (Co-Chief Scientist)	data info

Instruments

Isotope-ratio Mass Spectrometer

Supplied Name: Thermo Finnigan Delta V isotope ratio mass spectrometer.

Supplied Description:

Nitrate+nitrite d15N was measured using a Thermo Finnigan Delta V isotope ratio mass spectrometer.

Instrument Type

Generic Name: Isotope-ratio Mass Spectrometer

Acronym: IR Mass Spec; IRMS

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/LAB16/

Generic Description:

The Isotope-ratio Mass Spectrometer is a particular type of mass spectrometer used to measure the relative abundance of isotopes in a given sample (e.g. VG Prism II Isotope Ratio Mass-Spectrometer).

Parameters

Date and time formats are described in python strftime() syntax.

Supplied Name	Supplied description	Supplied Units	Standard Name
Cast	cast number	unitless	cast
Depth	depth of observation	meters	depth
Sigma_theta	potential density	kilograms per meter cubed (kg/m3)	sigma_theta
NO3_NO2	nitrate+nitrite concentration ([NO3-+NO2-])	micromole (uM)	NO3_NO2
NO3_NO2_d15N	nitrate+nitrite d15N (NO3-+NO2- d15N)	per mil	del15N_NO3NO2
NO3_NO2_d15N_1_SD	nitrate+nitrite d15N standard deviation	per mil	del15N_NO3NO2
Date	Date of observation in four digit year; 2 digit month; 2 digit day (yyyymmdd) format	unitless	date
Longitude	Longitude with west negative.	decimal degrees	lon
Latitude	Latitude with south negative.	decimal degrees	lat
Station	name of the station	unitless	station

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Database

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Dataset: OUTPACE - water column nitrate+nitrite