Dissolved nitrite and ammonium concentration data from R/V Atlantis (AT15-61) cruise in Jan-Feb 2010 and R/V Melville (MV1104) cruise in Mar-Apr 2011 in the Eastern Tropical South Pacific

Website: https://www.bco-dmo.org/dataset/820165
Data Type: Cruise Results
Version: 1
Version Date: 2020-08-06

» Expression of Microbial Nitrification in the Stable Isotopic Systematics of Oceanic Nitrite and Nitrate (Microbial Nitrification)
Casciotti, Karen L.Woods Hole Oceanographic Institution (WHOI)Lead Principal Investigator
Knapp, Angela N.Florida State University (FSU - EOAS)Scientist
Santoro, Alyson E.University of California-Santa Barbara (UCSB)Contact
Gerlach, Dana StuartWoods Hole Oceanographic Institution (WHOI BCO-DMO)BCO-DMO Data Manager

Dissolved nitrite ([NO2-]) and ammonium ([NH4+]) concentration data were collected on two cruises in the Eastern Tropical South Pacific. Data from R/V Atlantis (AT15-61) cruise collected in Jan-Feb 2010 and data from R/V Melville (MV1104) cruise collected in Mar-Apr 2011 as part of the Microbial Nitrification project.


Spatial Extent: N:-9.999 E:-79.985 S:-20 W:-100.001
Temporal Extent: 2010-01-31 - 2011-04-18

Acquisition Description

Seawater samples were obtained during the R/V Atlantis (AT15-61) and R/V Melville (MV1104) cruises in Jan-Feb 2010 and Mar-Apr 2011.  Water samples were collected at discrete depths using a standard 24-bottle Niskin rosette sampler equipped with an SBE9plus conductivity-temperature-depth (CTD) sensor package (SeaBird Electronics, Bellevue, WA). 

Ammonium concentration ([NH4+]) was determined on-ship in unfiltered 50 mL seawater samples using o-phthaldialdehyde derivatization (Holmes et al., 1999) and measurement on an Aquafluor 8000 handheld fluorometer (Turner Designs), with modifications as suggested in Taylor et al., 2007. Nitrite ([NO2-]) was determined on-ship in unfiltered 50 mL sample volumes using standard colorimetric methods (Strickland and Parsons, 1968).  NH4+ standards (30 – 300 nM) were freshly prepared for each analysis in duplicate using deep water (> 500 m) from the same station, which consistently had a lower blank than ultrapure water. Detection limits for [NH4+] and  [NO2-] were 0.010 µM, and 0.10 µM for [NO2-]. Measured values are reported even if they are lower than the detection limit.

Processing Description

Full protocol on seawater [NH4+] processing can be found below under Supplemental Files: "Ammonium Concentration in Seawater Protocol Santoro Lab v2.3"

BCO-DMO processing: 
- Adjusted parameter names to comply with database requirements. 
- Combined year, month, day fields into one date field. 
- Units in parentheses removed and added to Parameter Description metadata section. 
- Added a conventional header with dataset name, PI name, version date.
- Missing data identifier of 'NaN' replaced with 'nd'  ('nd' is BCO-DMO system default missing data identifier). 

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Supplemental Files

Ammonium Concentration in Seawater Protocol Santoro Lab v2.3
filename: Ammonium_Protocol_v2_3.pdf
(Portable Document Format (.pdf), 146.25 KB)
Protocol (v2.3) to determine Ammonium [NH4+] Concentration in Seawater used by the Santoro Lab (UCSB)

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Related Publications

Holmes, R. M., Aminot, A., Kérouel, R., Hooker, B. A., & Peterson, B. J. (1999). A simple and precise method for measuring ammonium in marine and freshwater ecosystems. Canadian Journal of Fisheries and Aquatic Sciences, 56(10), 1801–1808. doi:10.1139/f99-128
Santoro, A. E., Buchwald, C., Knapp, A. N., Berelson, W. M., Capone, D. G., & Casciotti, K. L. (2020). Nitrification and nitrous oxide production in the offshore waters of the Eastern Tropical South Pacific. doi:10.1002/essoar.10503499.1
Strickland, J.D.H and Parsons, T.R. (1968) A Practical Handbook of Seawater Analysis. Fisheries Research Board of Canada Bulletin 167, 71-75 [as seen in The Quarterly Review of Biology (1969) 44(3), 327–327. doi:10.1086/406210]
Taylor, B. W., Keep, C. F., Hall, R. O., Koch, B. J., Tronstad, L. M., Flecker, A. S., & Ulseth, A. J. (2007). Improving the fluorometric ammonium method: matrix effects, background fluorescence, and standard additions. Journal of the North American Benthological Society, 26(2), 167–177. https://doi.org/10.1899/0887-3593(2007)26[167:ITFAMM]2.0.CO;2.

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DepthSample depth meters
YearDeployment year unitless
MonthDeployment month (local) unitless
DayDeployment day (local) unitless
LatitudeLatitude of sample collection, South is negative decimal degrees
LongitudeLongitude of sample collection, West is negative decimal degrees
StationStation Number unitless
CastCast Number unitless
NO2Nitrite concentration micromole per liter (umol/L)
NH4Ammonium concentration micromole per liter (umol/L)
ISO_Date_LocalDate of sampling in ISO format (yyyy-mm-dd). Timezone was GMT-5 in 2010, GMT-4 in 2011 yyyy-mm-dd

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Dataset-specific Instrument Name
standard 24-bottle Niskin rosette sampler
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
SBE9plus conductivity-temperature-depth (CTD) sensor package
Generic Instrument Name
CTD Sea-Bird 9
Dataset-specific Description
SeaBird 9plus conductivity-temperature-depth (CTD) sensor package (SeaBird Electronics, Bellevue, WA).
Generic Instrument Description
The Sea-Bird SBE 9 is a type of CTD instrument package. The SBE 9 is the Underwater Unit and is most often combined with the SBE 11 Deck Unit (for real-time readout using conductive wire) when deployed from a research vessel. The combination of the SBE 9 and SBE 11 is called a SBE 911. The SBE 9 uses Sea-Bird's standard modular temperature and conductivity sensors (SBE 3 and SBE 4). The SBE 9 CTD can be configured with auxiliary sensors to measure other parameters including dissolved oxygen, pH, turbidity, fluorometer, altimeter, etc.). Note that in most cases, it is more accurate to specify SBE 911 than SBE 9 since it is likely a SBE 11 deck unit was used. more information from Sea-Bird Electronics

Dataset-specific Instrument Name
Turner Designs Aquafluor 8000 handheld fluorometer/turbidometer
Generic Instrument Name
Turner Designs Aquafluor 8000
Dataset-specific Description
AquaFluor® is a lightweight, inexpensive, handheld fluorometer/turbidimeter ideal for field use. Can be configured with one or two channels to measure turbidity, chlorophyll, algae, dyes, ammonium, CDOM, and more.  Detailed description at https://www.turnerdesigns.com/aquafluor-handheld-fluorometer 
Generic Instrument Description
The Turner Designs Aquafluor 8000 is a lightweight, handheld fluorometer/turbidimeter ideal for field use. It can be configured with one or two channels to measure turbidity, chlorophyll, algae, dyes, ammonium, CDOM, and more. Detailed description at https://www.turnerdesigns.com/aquafluor-handheld-fluorometer

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R/V Melville
Start Date
End Date
Samples collected between 10 and 20 S and 80 and 100 W.


R/V Atlantis
Start Date
End Date
This cruise provided the opportunity to expand the database the PI's are amassing on Synechococcus diversity and distribution for the NSF project “The role of iron (Fe) in controlling in situ distributions and activities of marine Synechococcus" (OCE-0825922) into an area that has not been well studied, and also provided the opportunity to test out hypotheses with controlled experimental manipulations of Fe, light, and temperature in the field. Science objectives: Documenting N2 fixation in N deficient waters of the Eastern Tropical South Pacific. Science Activities: Upper water column biogeochemistry, shallow and deep sediment trap deployment at six major (>24h) stations in the Peru Basin. Cruise information and original data are available from the NSF R2R data catalog.

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Project Information

Expression of Microbial Nitrification in the Stable Isotopic Systematics of Oceanic Nitrite and Nitrate (Microbial Nitrification)

Coverage: Eastern Tropical South Pacific

Description from NSF award abstract:
Closing the marine budgets of nitrate and nitrous oxide are central goals for researchers interested in nutrient-driven changes in primary productivity and climate change. With the implementation of new methods for oxygen isotopic analysis of seawater nitrate, it will be possible to construct a budget for nitrate based on its oxygen isotopic distribution that is complementary to nitrogen isotope budgets. Before we can effectively use oxygen isotopes in nitrate to inform the current understanding of the marine nitrogen cycle, we must first understand how different processes that produce (nitrification) and consume (assimilation, denitrification) nitrate affect its oxygen isotopic signature.

In this study, researchers at the Woods Hole Oceanographic Institution will provide a quantitative assessment of the oxygen isotopic systematics of nitrification in the field and thus fill a key gap in our understanding of 18O variations in nitrate, nitrite, and nitrous oxide. The primary goal is to develop a quantitative prediction of the oxygen isotopic signatures of nitrite and nitrate produced during nitrification in the sea. The researchers hypothesize that oxygen isotopic fractionation during nitrification is the primary factor setting the 18O values of newly produced nitrate and nitrite. Secondly, they hypothesize that oxygen atom exchange is low where ammonia oxidation and nitrite oxidation are tightly coupled, but may increase in regions with nitrite accumulation, such as in the primary and secondary nitrite maxima. They will test these hypotheses with a series of targeted laboratory and field experiments, as well as with measurements of nitrite and nitrate isotopic distributions extending through the euphotic zone, primary nitrite maximum, and secondary nitrite maximum of the Eastern Tropical South Pacific. The results of these experiments are expected to provide fundamental information required for the interpretation of 18O isotopic signatures in nitrite, nitrate, and N2O in the context of underlying microbial processes. A better understanding of these features and the processes involved is important for quantifying new production, controls on the N budget, and N2O production in the ocean -- which should lead to a better understanding of the direct and indirect interactions among the nitrogen cycle, marine chemistry, and climate.

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Funding SourceAward
NSF Division of Ocean Sciences (NSF OCE)

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