Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

These data appear in the following:

• Figure S7 of Santoro, et al. (2020)
• Table S5 of Santoro, et al. (2020)
• Figure S6 in pre-print on ESSOAr (doi.org/10.1002/essoar.10503499.1)

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). Samples for nucleic acid extraction and qPCR were collected from the rosette in 2-4 L polycarbonate bottles. Cells were harvested by pressure filtration onto 25 mm diameter, 0.2 µm pore-size polyethersulfone membrane filters (Supor-200, Pall Corporation, Port Washington, NY) housed in polypropylene filter holders (Whatman SwinLok, GE Healthcare, Pittsburgh, PA) using a peristaltic pump and silicone tubing. DNA was extracted according to Santoro,et al. (2010). For DNA extraction and analysis methods followed Santoro, et al. (2010). Sample volumes of 1-4 liters were filtered depending on the biomass present at each station and depth, and the filters were flash frozen in liquid nitrogen in 2 mL gasketed bead beating tubes (Fisher Scientific).

• Water samples were collected, filtered with peristaltic pressure onto 25 mm 0.2 µm pore size Supor filters.
• DNA was extracted according to Santoro et al. 2010.
• Abundance of bacterial amoA genes by quantitative PCR (qPCR) using SYBR Green chemistry followed that of Santoro et al. (2010).
• Abundance of archaeal amoA genes belonging to one of two ecotypes (WCA and WCB) were quantified using TaqMan assays following protocols described in Mosier and Francis (2011).
• Nitrospina-like 16S rRNA genes were quantified using the SYBR Green assay described in Mincer et al. (2007).

Data processing:  Reported abundances are the mean of triplicate qPCR reactions. Gene abundances per qPCR reaction were converted to abundance per liter of seawater using the volume of seawater filtered, the DNA extraction elution volume, and the volume of extract added to each reaction. Conversion assumes 100% DNA extraction efficiency.

BCO-DMO processing: 

• Added a conventional header with dataset name, PI name, version date
• 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.
• Default missing identifier of 'NaN' replaced with 'nd' ('nd' is BCO-DMO system default missing data identifier). 
• BDL (below detection limit) identifier maintained

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.