Methods for reproducible shipboard SFA nutrient measurement using RMNS and automated data processing

Abstract

Ocean observations are critical in developing our understanding of the interaction between the ocean and climate. Detailed information about the nutrient composition of the ocean is achieved using in situ sensing and the collection and analysis of physical samples from research vessels. The analysis of nutrients underpins work in understanding both the carbon cycle and biological productivity in oceans. Although in situ sensors are becoming more common for some nutrients, the best and most reliable method for making these measurements is to conduct analysis of physical samples at sea. This article discusses the analysis and data processing methods developed by the hydrochemistry team at Commonwealth Scientific and Industrial Research Organisation (CSIRO) to provide repeatable and accurate analysis of nutrient samples at sea. Nutrients are measured by segmented flow analysis and data are processed using in-house software (Hydrology Processor [HyPro]). These methods were used during the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) P15S voyage in 2016. Accuracy and precision of the analyses during the voyage was determined from measurement of the certified reference material for nutrients in seawater (RMNS) for silicate, phosphate, nitrate, and nitrite and is presented and discussed here. The accuracy of the silicate and phosphate RMNS measurements was within 1-3% of the certified values, and nitrate + nitrite within 1-2%. The precision for silicate, nitrate + nitrite, and phosphate was greater than 0.2%. The hydrochemistry team has established a standard operating procedure which assures the quality of nutrient data obtained is accurate and precise.

Mesozooplankton and Micronekton Active Carbon Transport in Contrasting Eddies

“…Water samples taken from the rosette at various depths were used to measure nutrients and calibrate oxygen and chlorophyll a from the CTD. Dissolved inorganic nutrient measurements were made using automated continuous flow with colorimetric detection following CSIRO standard operating procedures (Rees et al, 2018). Fluorescence was converted to chlorophyll a concentrations through regression analyses as described in 1 http://imos.aodn.org.au/imos/ Roughan et al (2017) for 2015 samples (r 2 = 0.81, n = 66) and Henschke et al (2019) for 2017 samples (r 2 = 0.84, n = 20) to provide full water column chlorophyll a estimates.…”

Resupply of mesopelagic dissolved iron controlled by particulate iron composition

“…(TM-)RESPIRE procedure -RESPIRE were cleaned following ref. 22 Dissolved nutrients were analysed onboard with a segmented flow analyser (AAIII HR Seal Analytical; detection limits were 0.02 μM for P, 0.05 μM for N, and 0.08 μM for Si) 50,51 .…”

Sea Ice Meltwater and Circumpolar Deep Water Drive Contrasting Productivity in Three Antarctic Polynyas

“…Bottle salinity was determined onboard by conductivity measured with the Guildline Autosal, with a precision of ±0.002 g/kg. Nitrate and nitrite (NO x ), silicic acid, phosphate, and ammonium concentrations were determined four months postcruise at the CSIRO laboratory (Hobart, Australia) with a Seal AA3 segmented flow instrument following the methods of Wood et al (), Armstrong et al (), Murphy and Riley (), and Kérouel and Aminot (), respectively (Rees et al, ). Samples had been frozen at −20 °C for NO x , phosphate, and ammonia and refrigerated for silicic acid, which may have induced errors.…”