An updated version of the global interior ocean biogeochemical data product, GLODAPv2.2021
Authors: Lauvset Siv K. , Lange Nico , Tanhua Toste , Bittig Henry C. , Olsen Are , Kozyr Alex , Álvarez Marta , Becker Susan , Brown Peter J. , Carter Brendan R. , Cotrim da Cunha Leticia , Feely Richard A. , van Heuven Steven , Hoppema Mario , Ishii Masao , Jeansson Emil , Jutterström Sara , Jones Steve D. , Karlsen Maren K. , Lo Monaco Claire , Michaelis Patrick , Murata Akihiko , Pérez Fiz F. , Pfeil Benjamin , Schirnick Carsten , Steinfeldt Reiner , Suzuki Toru , Tilbrook Bronte , Velo Anton , Wanninkhof Rik , Woosley Ryan J. , Key Robert M. 
Published: December 2021

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.