Abstract

Abstract. The Global Ocean Data Analysis Project (GLODAP) is a synthesis effort providing regular compilations of surface-to-bottom ocean biogeochemical bottle data, with an emphasis on seawater inorganic carbon chemistry and related variables determined through chemical analysis of seawater samples. GLODAPv2.2021 is an update of the previous version, GLODAPv2.2020 (Olsen et al., 2020). The major changes are as follows: data from 43 new cruises were added, data coverage was extended until 2020, all data with missing temperatures were removed, and a digital object identifier (DOI) was included for each cruise in the product files. In addition, a number of minor corrections to GLODAPv2.2020 data were performed. GLODAPv2.2021 includes measurements from more than 1.3 million water samples from the global oceans collected on 989 cruises. The data for the 12 GLODAP core variables (salinity, oxygen, nitrate, silicate, phosphate, dissolved inorganic carbon, total alkalinity, pH, CFC-11, CFC-12, CFC-113, and CCl4) have undergone extensive quality control with a focus on systematic evaluation of bias. The data are available in two formats: (i) as submitted by the data originator but updated to World Ocean Circulation Experiment (WOCE) exchange format and (ii) as a merged data product with adjustments applied to minimize bias. For this annual update, adjustments for the 43 new cruises were derived by comparing those data with the data from the 946 quality controlled cruises in the GLODAPv2.2020 data product using crossover analysis. Comparisons to estimates of nutrients and ocean CO2 chemistry based on empirical algorithms provided additional context for adjustment decisions in this version. The adjustments are intended to remove potential biases from errors related to measurement, calibration, and data handling practices without removing known or likely time trends or variations in the variables evaluated. The compiled and adjusted data product is believed to be consistent with to better than 0.005 in salinity, 1 % in oxygen, 2 % in nitrate, 2 % in silicate, 2 % in phosphate, 4 µmol kg−1 in dissolved inorganic carbon, 4 µmol kg−1 in total alkalinity, 0.01–0.02 in pH (depending on region), and 5 % in the halogenated transient tracers. The other variables included in the compilation, such as isotopic tracers and discrete CO2 fugacity (fCO2), were not subjected to bias comparison or adjustments. The original data, their documentation, and DOI codes are available at the Ocean Carbon Data System of NOAA NCEI (https://www.ncei.noaa.gov/access/ocean-carbon-data-system/oceans/GLODAPv2_2021/, last access: 7 July 2021). This site also provides access to the merged data product, which is provided as a single global file and as four regional ones – the Arctic, Atlantic, Indian, and Pacific oceans – under https://doi.org/10.25921/ttgq-n825 (Lauvset et al., 2021). These bias-adjusted product files also include significant ancillary and approximated data and can be accessed via https://www.glodap.info (last access: 29 June 2021). These were obtained by interpolation of, or calculation from, measured data. This living data update documents the GLODAPv2.2021 methods and provides a broad overview of the secondary quality control procedures and results.

Highlights

  • The oceans mitigate climate change by absorbing both atmospheric CO2 corresponding to a significant fraction of anthropogenic CO2 emissions (Friedlingstein et al, 2019; Gruber et al, 2019) and most of the excess heat in the Earth system caused by the enhanced greenhouse effect (Cheng et al, 2020, 2017)

  • All identified offsets were scrutinized by the Global Ocean Data Analysis Project (GLODAP) reference group through a series of teleconferences during April 2021 in order to decide the adjustments to be applied to correct for the offset

  • The TCO2 data measured on this cruise are 2.15 ± 1.04 μmol kg−1 higher when compared to the data measured on nearby cruises included in GLODAPv2.2020

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Summary

Introduction

The oceans mitigate climate change by absorbing both atmospheric CO2 corresponding to a significant fraction of anthropogenic CO2 emissions (Friedlingstein et al, 2019; Gruber et al, 2019) and most of the excess heat in the Earth system caused by the enhanced greenhouse effect (Cheng et al, 2020, 2017). The objective of GLODAP (Global Ocean Data Analysis Project; https://www.glodap.info, last access: 29 June 2021) is to ensure provision of high-quality and biascorrected water column bottle data from the ocean surface to bottom These data document the state and the evolving changes in physical and chemical ocean properties, e.g., the inventory of the excess CO2 in the ocean, natural oceanic carbon, ocean acidification, ventilation rates, oxygen levels, and vertical nutrient transports (Tanhua et al, 2021). Full updates involve a reanalysis, notably crossover and inversion, of the entire dataset (both historical and new cruises) and all data points are subject to potential adjustment Recently available data are added following quality control procedures to ensure their consistency with the cruises included in the latest GLODAP release. The third intermediate update is presented here, which adds data from 43 new cruises to the last update, GLODAPv2.2020 (Olsen et al, 2020)

Key features of the update
Data assembly and primary quality control
Secondary quality control
Merging of sensor and bottle data
Crossover analyses
Other consistency analyses
CANYON-B and CONTENT analyses
Halogenated transient tracers
Merged product generation
Merging
Secondary quality control results and adjustments
Sensor and bottle data merge for salinity and oxygen
Adjustment summary
Findings
Summary
Full Text
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