A rare intercomparison of nutrient analysis at sea: lessons learned and recommendations to enhance comparability of open-ocean nutrient data

Abstract

An intercomparison study has been carried out on the analysis of inorganic nutrients at sea following the operation of two nutrient analysers simultaneously on the GO-SHIP A02 trans-Atlantic survey in May 2017. Both instruments were Skalar San ++ Continuous Flow Analyzers, one from the Marine Institute, Ireland and the other from Dalhousie University, Canada, each operated by their own laboratory analysts following GO-SHIP guidelines while adopting their existing laboratory methods. There was high comparability between the two data sets and vertical profiles of nutrients also compared well with those collected in 1997 along the same A02 transect by the World Ocean Circulation Experiment. The largest differences between data sets were observed in the low-nutrient surface waters and results highlight the value of using three reference materials (low, middle and high concentration) to cover the full range of expected nutrients and identify bias and non-linearity in the calibrations. The intercomparison also raised some interesting questions on the comparison of nutrients analysed by different systems and a number of recommendations have been suggested that we feel will enhance the existing GO-SHIP guidelines to improve the comparability of global nutrient data sets. A key recommendation is for the specification of clearly defined data quality objectives for oceanic nutrient measurements and a flagging method for reported data that do not meet these criteria.The A02 nutrient data set is currently available at the National Oceanographic Data Centre of Ireland: https://doi.

Biodegradation of Terrigenous Organic Matter in a Stratified Large-Volume Water Column: Implications of the Removal of Terrigenous Organic Matter in the Coastal Ocean

“…The depth profile of temperature and salinity was regularly measured with a Xylem EXO water-quality sonde (YSI Inc., a Xylem brand, USA). Samples for DIN were measured on a Skalar San ++ continuous flow analyzer with an established method . DOC was measured with the Winkler method .…”

“…Samples for DIN were measured on a Skalar San ++ continuous flow analyzer with an established method. 31 DOC was measured with the Winkler method. 32 In phase II, apparent oxygen utilization (AOU) of the bottom seawater samples was calculated as the difference between the saturation oxygen concentration and the Winker oxygen content.…”

Glaciers and Nutrients in the Canadian Arctic Archipelago Marine System

“…Nutrient concentrations were analyzed within 1 month of collection on a Skalar SAN++ Continuous Flow Nutrient Analyzer at the CERC. OCEAN Laboratory (McGrath et al., 2019). The limits of detections for NO 3 − , NO 2 − , NH 3 + , PO 4 3− , and SiO 4 concentrations were 0.3, 0.15, 0.01, 0.2, and 0.08 μM respectively.…”

“…Nutrient concentrations were analyzed within 1 month of collection on a Skalar SAN++ Continuous Flow Nutrient Analyzer at the CERC. OCEAN Laboratory (McGrath et al, 2019) Samples for total dissolvable metals were first collected from the GO-FLO bottle water on deck before any other water samples were acquired. Wearing trace metal grade gloves, we rinsed the GO-FLO spigot with dilute trace metal clean HCl and then 3x rinsed and filled trace metal clean 60 mL high density polyethyl-ene (HDPE) bottles with unfiltered water, directly from the cleaned spigot.…”

Nutrient and Carbon Export From a Tidewater Glacier to the Coastal Ocean in the Canadian Arctic Archipelago

“…Reagents and samples, segmented with air bubbles, were pumped through a manifold for mixing and heating before entering the flow cell. Nitrite, nitrate, phosphate, and silicate concentrations were detected colorimetrically with optical background correction, while ammonia concentrations were determined with a fluorometer; in both cases, matrix‐matched (artificial seawater) calibration standards were used (McGrath et al., 2019). LODs for nitrite, nitrate, ammonia, phosphate, silicate were: 0.3, 0.15, 0.01, 0.2, and 0.08 μM, respectively.…”