DOI: 10.5061/dryad.prr4xgxxf
title: Concentration and δ15N of amino acids in size-fractionated particles from the eastern tropical North Pacific ODZ

description: This dataset includes the concentration and δ15N of bulk N and
 amino acids in size-fractionated particles. Particle samples were
 collected aboard the R/V Sally Ride (cruise SR2011) from December 23 – 30,
 2020 with a McLane large volume pumping system (WTS-LV). These data assess
 the N sources utilized by different phytoplankton communities inhabiting
 the two chlorophyll maxima and the transformation of particulate organic
 matter within the oxygen-deficient zone.
description: Two particle fractions were collected at five stations in the
 eastern tropical North Pacific region. At each station, seawater was
 filtered sequentially through a 53 µm Nitex mesh and then a pre-combusted
 142-mm-diameter glass fiber filter (GF-75: 0.3 µm retention size; or GF/F:
 0.7 µm nominal retention size) with the McLane pump in situ. These filters
 were promptly frozen upon retrieval.<br>Each 53 µm Nitex mesh was
 immersed in approximately 100 ml of MilliQ water and subjected to a
 5-minute sonication. The solution was filtered onto pre-combusted 47-mm
 glass fiber filters (GF/F, 0.7 µm pore size), which retain the &gt; 53
 µm particle fraction. The GF-75 and GF/F filters (0.3
 or 0.7 – 53 µm fractions) were subsampled, packed in tin capsules, and
 analyzed for concentration and δ<sup>15</sup>N of bulk
 materials by an elemental analyzer isotope-ratio mass spectrometer at the
 UC Davis Stable Isotope Facility. Bulk δ<sup>15</sup>N
 analysis was not performed for the &gt; 53 µm fraction due to the
 limited amount of collected material. The sample
 pre-treatment procedures for δ<sup>15</sup>N-amino acids were
 based on the method detailed in Zhang et al. (2021). The glass fiber
 filters underwent hydrolysis with 6N HCl for 22 hours at 110°C.
 Hydrophobic impurities were eliminated from the hydrolysates through
 liquid-liquid extraction using n-hexane/dichloromethane (6:5, v/v),
 followed by evaporation to dryness in a vacuum evaporator (RapidVap,
 Labconco). The samples were subsequently redissolved in 0.05N HCl and
 further purified via cation-exchange resin, following procedures adapted
 from Takano et al. (2010) to remove metal ions and salts. The purified
 amino acids in the samples were completely dried under vacuum.
 Amino acids in the samples were separated and collected as
 individual fractions using an ICS-5000+ Ion-exchange chromatography system
 with the instrumental method adapted from Zhang et al. (2021). For each
 sample, Phe, Glu, and their corresponding IC procedural blanks were
 collected from 1 – 3 replicate injections. The IC-collected fractions were
 sequentially converted to
 NO<sub>2</sub><sup>-</sup> and
 N<sub>2</sub>O through a two-step process involving
 hypochlorite oxidation and azide reduction, as described in McIlvin and
 Altabet (2005); Zhang et al. (2007); Zhang and Altabet (2008); and Zhang
 et al. (2021). δ<sup>15</sup>N-N<sub>2</sub>O was
 determined with a GV IsoPrime IRMS.
description: # Concentration and δ15N of amino acids in size-fractionated particles
 from the eastern tropical North Pacific ODZ
 [https://doi.org/10.5061/dryad.prr4xgxxf](https://doi.org/10.5061/dryad.prr4xgxxf) ## Description of the data and file structure This dataset includes the concentration and δ15N of bulk N and amino acids in size-fractionated particles. Two particle fractions were collected aboard the R/V Sally Ride (cruise SR2011) from December 23 – 30, 2020 at five stations with a McLane large volume pumping system (WTS-LV). These data assess the N sources utilized by different phytoplankton communities inhabiting the two chlorophyll maxima and the transformation of particulate organic matter within the oxygen-deficient zone. Two particle fractions were collected at five stations in the eastern tropical North Pacific region. At each station, seawater was filtered sequentially through a 53 µm Nitex mesh and then a pre-combusted 142-mm-diameter glass fiber filter (GF-75: 0.3 µm retention size; or GF/F: 0.7 µm nominal retention size) with the McLane pump in situ. Each 53 µm Nitex mesh was immersed in approximately 100 ml of MilliQ water and subjected to a 5-minute sonication. The solution was filtered onto pre-combusted 47-mm glass fiber filters (GF/F, 0.7 µm pore size), which retain the &gt; 53 µm particle fraction. The GF-75 and GF/F filters (0.3 or 0.7 – 53 µm fractions) were subsampled, packed in tin capsules, and analyzed for concentration and δ15N of bulk materials by an elemental analyzer isotope-ratio mass spectrometer at the UC Davis Stable Isotope Facility. Bulk δ15N analysis was not performed for the &gt; 53 µm fraction due to the limited amount of collected material.  Amino acids in the samples were separated and collected as individual fractions using an ICS-5000+ Ion-exchange chromatography system. For each sample, Phe, Glu, and their corresponding IC procedural blanks were collected from 1 – 3 replicate injections. The IC-collected fractions were sequentially converted to NO2- and N2O through a two-step process involving hypochlorite oxidation and azide reduction. δ15N-N2O was determined with a GV IsoPrime IRMS. Concentrations of Phe and Glu in the particle samples were determined by calibrating them against the chromatographic peak areas of a set of amino acid standard mixtures at varying concentration levels between 1 – 5 mM. The δ15N of Phe and Glu were calibrated by three replicate injections of multiple amino acid isotopic standard mixtures with distinct δ15N values were carried out as outlined in Zhang et al. (2021). Trophic position (TP) was calculated from δ15N of Phe and Glu with an empirical formula proposed by Chikaraishi et al. (2009). Standard deviations were reported for samples with δ15N measurements obtained from replicate IC injections. The error propagated from uncertainties of the instrument, calibration, and correction was calculated for samples collected from a single injection. ### Files and variables #### File: ETNP-ODZ\_AAd15N\_data\_final.xlsx **Description:**  ##### Variables * Date, "Sampling date (UTC); format: YYYY-MM-DD", unitless * Time, "Sampling time (UTC); format: hh:mm:ss", unitless * Lat, "Latitude in decimal degrees North", decimal degrees North * Lon, "Longitude in decimal degrees West", decimal degrees West * Station, “Sampling station number”, unitless * Size_fraction, “Size fraction of particles”, µm * Depth, “Depth of sample collection”, meter (m) * Bulk N, “Concentration of bulk N”, nmol/L * Phe, “Concentration of phenylalanine”, nmol/L * Glu, “Concentration of glutamic acid”, nmol/L * bulk_d15N, “d15N of bulk N”, per mil (‰) relative to air * d15N-Phe, “d15N of phenylalanine”, per mil (‰) relative to air * d15N_Phe_sd, “Standard deviation of d15N of phenylalanine”, per mil (‰) relative to air * d15N-Glu, “d15N of glutamic acid”, per mil (‰) relative to air * d15N_Glu_sd, “Standard deviation of d15N of glutamic acid”, per mil (‰) relative to air * TP, “Trophic position”, unitless * TP_sd, “Standard deviation of trophic position”, unitless  / = no data value\ \# = below detection limit