Global certified-reference-material- or reference-material-scaled nutrient gridded dataset GND13

Michio Aoyama

doi:10.5194/essd-12-487-2020

Abstract

Abstract. A global nutrient gridded dataset that might be the basis for studies of more accurate spatial distributions of nutrients in the global ocean was created and named GND13. During 30 cruises, reference materials of nutrients in seawater or their equivalents were used at all stations, and high-precision measurements were made. The precision of the nutrient analyses was better than 0.2 %. Data were collected from the hydrographic cruises in the JASMTEC R/V Mirai cruises, JMA cruise, CARINA, PACIFICA, and WGHC datasets from which nutrient data were available. Analyses were conducted at 243 crossover stations. Cruises that used certified reference materials or reference materials (CRMs/RMs) for seawater nutrient concentration measurements were used as a reference of an unbroken chain of comparison to determine correction factors which made nutrient concentrations obtained by other cruises SI traceable. Dissolved oxygen was secondarily quality-controlled using the same methodology as was used to create the nutrient gridded data product, but, lacking a traceable standard, the resulting oxygen data product is not SI traceable. Finally, a dataset of nitrate, phosphate, and silicate concentrations was created at latitude and longitude intervals of 0.5∘ and on 136 isobaric surfaces to depths of 6500 m as an SI-traceable dataset. This dataset has already been published at: https://doi.org/10.17596/0000001 (Aoyama, 2017).

Highlights

Global oceanic biogeochemical cycles are being significantly altered by the direct and indirect impacts of human activities.It is necessary to obtain accurate information about changes and trends of concentrations of inorganic carbon and dissolved inorganic nutrients in both shallow and deep ocean waters
For this information to be of practical use, it is critical that results from different laboratories can be compared with complete confidence
A global consensus about nutrient concentrations requires that there be access to certified reference materials (CRMs), and there must be a requirement or ethos for the use of these CRMs when oceanic nutrient concentrations are measured and subsequently when they are recorded in global databases, incorporated in climate models, and used to quantify changes to the Earth system

Summary

Introduction

Global oceanic biogeochemical cycles are being significantly altered by the direct and indirect impacts of human activities. Consensus standard deviations of nutrient concentrations of nitrate, phosphate, and silicate were 1 order of magnitude larger than the homogeneity of the currently available CRM/RMs and were about double the reported precision of measurements of the individual laboratories These IC results showed that use of CRMs should greatly improve the comparability of nutrient data among laboratories throughout the world. This article is an effort to establish a global nutrient dataset for which comparability and traceability in space and time are explicitly ensured based on the use of CRMs/RMs of nutrients in seawater Another positive attribute of this work is that the uncertainty of correction factors could be estimated

Methods and data

Findings

Conclusions