Wintertime nitrate delta 15N and delta 18O from hydrocasts from R/V S. A. Agulhas II cruise VOY03 in the Southern Ocean south of Africa in 2012 (Diatom-bound_N_Isotopes project)

Website: https://www.bco-dmo.org/dataset/557616
Version: 05 May 2015
Version Date: 2015-05-05

Project
» High-resolution, Assemblage-specific Records of Diatom-bound N Isotopes from the Indian Sector of the Antarctic Ocean (Diatom-bound_N_Isotopes)
ContributorsAffiliationRole
Sigman, Daniel M.Princeton UniversityPrincipal Investigator
Smart, Sandi M.Stellenbosch UniversityContact
Rauch, ShannonWoods Hole Oceanographic Institution (WHOI BCO-DMO)BCO-DMO Data Manager


Dataset Description

Wintertime nitrate delta 15N and delta 18O from the Southern Ocean south of Africa from hydrocasts taken on the July 2012 R/V S.A. Agulhas II VOY03 expedition. The dataset includes hydrocast (depth-profile) data along with the hydrographic data accompanying each CTD.

 

Note: In addition to the awards identified below, the dataset was also supported by funding from the South African National Research Foundation (NRF), Applied Centre for Climate and Earth Systems Science (ACCESS), University of Cape Town (UCT), and the Grand Challenges Program of Princeton University.


Acquisition Description

Samples were collected aboard the R/V S.A. Agulhas II and analyzed in the Sigman lab at Princeton University using the "denitrifier method" to convert sample nitrate to N2O gas. The isotopic composition of N2O was measured by GC-IRMS using a Thermo MAT 253 mass spectrometer with a purpose-built on-line N2O extraction and purification system. For the nitrate+nitrite data, the pooled sample standard deviation is 0.05‰ for delta 15N (n = 3-7) and 0.17‰ for delta 18O (n = 3-5). For the ‘nitrate-only’ data, the pooled sample standard deviation is 0.05‰ for delta 15N (n = 3-7) and 0.13‰ for delta 18O (n = 3-7). See methods section of Smart et al. (2015) for details of sample collection, isotope analysis and data quality.

Related Publications:
Smart, S.M., S.E. Fawcett, S.J. Thomalla, M.A. Weigand, C.J.C. Reason, and D.M. Sigman. 2015. Isotopic evidence for nitrification in the Antarctic winter mixed layer, Global Biogeochem. Cycles, 29, doi: 10.1002/2014GB005013.


Processing Description

Individual sample analyses were referenced against automated injections of N2O from a gas cylinder; however, the N2O cylinder is not used as the absolute reference. Rather, each sample run included replicates of two international reference materials, IAEA-N3 and USGS-34 that were used to calibrate isotope ratios to that of N2 in air (for delta 15N) and VSMOW (for delta 18O). An in-house N2O standard was also run with each batch of samples to monitor mass spectrometry. See methods section of Smart et al. (2015) for a description of the procedures followed.

BCO-DMO Processing Notes:
- Modified parameter names to conform with BCO-DMO naming conventions.
- Replaced blanks (missing data) with 'nd', meaning 'no data'.


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Parameters

ParameterDescriptionUnits
stationStation number. dimensionless
dateMonth, day, and year of sampling. mm/dd/yy
timeTime, in hours and minutes, of sampling. HHMM
latLatitude in decimal degrees North. (Negative values = South). decimal degrees
lonLongitude in decimal degrees East. decimal degrees
depth_mixed_layerMixed layer calculated from sigma-t using ref depth = 32 m. Mixed layer depth at each station is defined as the closest depth to the surface at which sigma theta is greater by >= 0.03 kg m-3 than the value at a reference depth of 32 m (the shallowest depth common to every CTD station) (based on the criterion of de Boyer Montégut et al. (2004)). meters
sampleSample ID number. dimensionless
depthSample depth. meters
tempWater temperature. degrees Celsius ( C)
salSalinity. practical salinity units (psu)
oxygen_corrOxygen (corrected). milliliters per liter (ml/l)
sigma_tPotential density (sigma-theta); calculated from temperature and salinity. kilograms per cubic meter (kg/m^3)
NO3_NO2_meanMean nitrate (NO3) plus nitrite (NO2) concentration of a sample in micromolar units. micromolar (uM)
NO3_NO2_stdevStandard deviation of the nitrate (NO3) plus nitrite (NO2) concentration of a sample in micromolar units. micromolar (uM)
d15N_NO3_NO2_meandelta 15N of NO3+NO2. d15N (‰ vs. AIR) is the nitrogen isotopic composition of a sample expressed in delta notation (in units of per mil) relative to atmospheric N2, where delta 15N = {[ (15N/14N)sample / (15N/14N)atmN2 ] – 1} × 1000. per mil
d15N_NO3_NO2_stdevStandard deviation of d15N_NO3_NO2_mean. per mil
d18Ocorr_NO3_NO2_meandelta 18O of NO3+NO2. d18O (‰ vs. VSMOW) is the oxygen isotopic composition of a sample expressed in delta notation (in units of per mil) relative to Vienna Standard Mean Ocean Water (VSMOW), where delta 18O = {[ (18O/16O)sample / (18O/16O)VSMOW ] – 1} × 1000. per mil
d18O_NO3_NO2_stdevStandard deviation of d18O_NO3_NO2_mean. per mil
NO3_meanMean nitrate (NO3) concentration of a sample in micromolar units, measured after nitrite (NO2) had been removed (using the protocol of Granger and Sigman (2009)). micromolar (uM)
NO3_stdevStandard deviation of the nitrate (NO3) concentration of a sample in micromolar units, measured after nitrite (NO2) had been removed (using the protocol of Granger and Sigman (2009)). micromolar (uM)
d15N_NO3_meandelta 15N of NO3. d15N (‰ vs. AIR) is the nitrogen isotopic composition of a sample expressed in delta notation (in units of per mil) relative to atmospheric N2, where delta 15N = {[ (15N/14N)sample / (15N/14N)atmN2 ] – 1} × 1000. per mil
d15N_NO3_stdevStandard deviation of d15N_NO3_mean. per mil
d18O_NO3_meandelta 18O of NO3. d18O (‰ vs. VSMOW) is the oxygen isotopic composition of a sample expressed in delta notation (in units of per mil) relative to Vienna Standard Mean Ocean Water (VSMOW), where delta 18O = {[ (18O/16O)sample / (18O/16O)VSMOW ] – 1} × 1000. per mil
d18O_NO3_stdevStandard deviation of d18O_NO3_mean. per mil
month2-digit month of year. mm (01 to 12)
day2-digit day of month. dd (01 to 31)
year4-digit year. YYYY
ISO_DateTime_UTCDate and time (UTC) formatted to ISO 8601 standard, where T indicates the start of the time string and Z indicates UTC. YYYY-mm-ddTHH:MM:SS.xxZ


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Instruments

Dataset-specific Instrument Name
Niskin bottle
Generic Instrument Name
Niskin bottle
Generic Instrument Description
A Niskin bottle (a next generation water sampler based on the Nansen bottle) is a cylindrical, non-metallic water collection device with stoppers at both ends. The bottles can be attached individually on a hydrowire or deployed in 12, 24, or 36 bottle Rosette systems mounted on a frame and combined with a CTD. Niskin bottles are used to collect discrete water samples for a range of measurements including pigments, nutrients, plankton, etc.

Dataset-specific Instrument Name
CTD
Generic Instrument Name
CTD Sea-Bird
Dataset-specific Description
Circumpolar fronts were identified from surface and subsurface (200m) temperature and salinity properties using data obtained from a Sea-Bird conductivity-temperature-depth (CTD) sensor mounted on the Niskin bottle rosette, as well as from 28 underway-CTD and 88 expendable bathythermograph deployments.
Generic Instrument Description
Conductivity, Temperature, Depth (CTD) sensor package from SeaBird Electronics, no specific unit identified. This instrument designation is used when specific make and model are not known. See also other SeaBird instruments listed under CTD. More information from Sea-Bird Electronics.

Dataset-specific Instrument Name
Sea-Bird SBE 43
Generic Instrument Name
Sea-Bird SBE 43 Dissolved Oxygen Sensor
Dataset-specific Description
Dissolved oxygen profiles (obtained for every CTD cast from a mounted Sea-Bird SBE 43 sensor) were used together with potential density, salinity, and nitrate profiles to identify key water masses.
Generic Instrument Description
The Sea-Bird SBE 43 dissolved oxygen sensor is a redesign of the Clark polarographic membrane type of dissolved oxygen sensors. more information from Sea-Bird Electronics


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Deployments

VOY03

Website
Platform
R/V S.A. Agulhas II
Start Date
2012-07-10
End Date
2012-08-06
Description
R/V S.A. Agulhas II, VOY03 (July 2012): The winter "shake‐down" cruise, part of the GoodHope monitoring programme. Transect extends from the subtropics (offshore of Cape Town, South Africa; 33.9°S, 18.4°E) to just beyond the winter sea-ice edge (encountered at 56.7°S, 0.0°E), covering a 0-2000 m depth range.


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Project Information

High-resolution, Assemblage-specific Records of Diatom-bound N Isotopes from the Indian Sector of the Antarctic Ocean (Diatom-bound_N_Isotopes)

Coverage: Kerguelen Plateau


Description from NSF award abstract:
The high concentration of the major nutrients nitrate and phosphate is a fundamental characteristic of the Antarctic Zone in the Southern Ocean and is central to its role in global ocean fertility and the global carbon cycle. The isotopic composition of diatom-bound organic nitrogen is one of the best hopes for reconstructing the nutrient status of polar surface waters over glacial cycles, which in turn may hold the explanation for the decline in atmospheric carbon dioxide during ice ages. The PIs propose to generate detailed diatom-bound nitrogen isotope (δ15Ndb) records from high sedimentation rate cores from the Kerguelen Plateau. Because the cores were collected at relatively shallow seafloor depths, they have adequate planktonic and benthic foraminifera to develop accurate age models. The resulting data could be compared with climate records from Antarctic ice cores and other archives to investigate climate-related changes, including the major steps into and out of ice ages and the millennial-scale events that occur during ice ages and at their ends. The records generated in this project will provide a critical test of hypotheses for the cause of lower ice age CO2.

This study will contribute to the goal of understanding ice ages and past CO2 changes, which both have broad implications for future climate. Undergraduates will undertake summer internships, with the possibility of extending their work into junior year projects and senior theses. In addition, the PI will lead modules for two Princeton programs for middle school teachers and will host a teacher for a six-week summer research project.



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Funding

Funding SourceAward
NSF Division of Ocean Sciences (NSF OCE)
NSF Division of Polar Programs (NSF PLR)
NSF Division of Polar Programs (NSF PLR)
NSF Division of Ocean Sciences (NSF OCE)
European Commission Seventh Framework Program (FP7-ENV-2010)

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