Dataset: Zooplankton CSIA-AA

We conducted double oblique zooplankton net tows from 200 m water depth to the sea-surface using a 0.7 m-diameter Bongo frame with paired 200-µm mesh nets, equipped with two General Oceanics flow meters to measure the filtered volume and a temperature-depth recorder. A fraction of each tow was size-fractionated through nested sieves (4-mm, 2-mm, 1-mm, 0.5-mm, 0.2-mm), rinsed with isotonic ammonium formate, and stored for isotopic analyses. Samples were then dried, fumed with HCl (to remove calcium carbonate), packed in pre-combusted tins and shipped to the U.C. Davis Stable Isotope Facility.

Per the U.C. Davis Stable Isotope Facility analytical methods are as follows:

Amino acids are made suitable for gas chromatography by derivatization as N-acetyl methyl esters

(NACME[1]). Prior to derivatization, amino acids are liberated from sample material proteins by acid hydrolysis (6 M HCl, 70 min, 150 ºC under N2 headspace). Additional purification steps, such as strong cation-exchange chromatography (SCX; Dowex 50WX8 resin), may be required for sample materials with significant fractions of carbohydrates, lipids, salts, or other potential matrix interferences. NACME amino acid derivatives are injected at 260 ºC (splitless, 1 min) and separated on an Agilent DB-35 column (60 m x 0.32 mm ID x 1.5 µm film thickness) at a constant flow rate of 2 mL/min under the following temperature program: 70 °C (hold 2 min); 140 °C (15 °C/min, hold 4 min); 240 °C (12 °C/min, hold 5 min); and 255 °C (8 °C/min, hold 35 min).

GC-C-IRMS is performed on a Thermo Trace GC 1310 gas chromatograph coupled to a Thermo Scientific Delta V Advantage isotope-ratio mass spectrometer via a GC IsoLink II combustion interface. The combustion reactor is a NiO tube containing CuO and NiO wires maintained at 1000 °C. Water is subsequently removed through a Nafion dryer before the analyte gases are transferred to the IRMS.

During 15N analysis, CO2 is removed from the post-combustion carrier stream through the use of a liquid nitrogen trap to prevent isobaric interferences within the ion source.

All samples are analyzed in duplicate; further replicates may be analyzed if initial measurements fall outside expected measurement error. Replicates of the quality control and assurance reference materials are measured every five samples.

Instruments:
Thermo Trace GC 1310 gas chromatograph coupled to a Thermo Scientific Delta V Advantage isotope-ratio mass spectrometer via a GC IsoLink II combustion interface.