An updated version of the global interior ocean biogeochemical data product, GLODAPv2.2020
Authors: Olsen Are , Lange Nico , Key Robert M. , Tanhua Toste , Bittig Henry C. , Kozyr Alex , Álvarez Marta , Azetsu-Scott Kumiko , 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 , Landa Camilla S. , Lauvset Siv K. , Michaelis Patrick , Murata Akihiko , Pérez Fiz F. , Pfeil Benjamin , Schirnick Carsten , Steinfeldt Reiner , Suzuki Toru , Tilbrook Bronte , Velo Anton , Wanninkhof Rik , Woosley Ryan J. 
Published: December 2020

Abstract. The Global Ocean Data Analysis Project (GLODAP) is a
synthesis effort providing regular compilations of surface-to-bottom ocean
biogeochemical data, with an emphasis on seawater inorganic carbon chemistry
and related variables determined through chemical analysis of seawater
samples. GLODAPv2.2020 is an update of the previous version, GLODAPv2.2019.
The major changes are data from 106 new cruises added, extension of time
coverage to 2019, and the inclusion of available (also for historical
cruises) discrete fugacity of CO2 (fCO2) values in the merged
product files. GLODAPv2.2020 now includes measurements from more than 1.2 million water samples from the global oceans collected on 946 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 WOCE
exchange format and (ii) as a merged data product with adjustments applied
to minimize bias. These adjustments were derived by comparing the data from
the 106 new cruises with the data from the 840 quality-controlled cruises of
the GLODAPv2.2019 data product using crossover analysis. Comparisons to
empirical algorithm estimates provided additional context for adjustment
decisions; this is new to 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 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 fCO2, were not
subjected to bias comparison or adjustments. The original data and their documentation and DOI codes are available at the
Ocean Carbon Data System of NOAA NCEI
(https://www.nodc.noaa.gov/ocads/oceans/GLODAPv2_2020/, last
access: 20 June 2020). 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/10.25921/2c8h-sa89 (Olsen et al., 2020). These
bias-adjusted product files also include significant ancillary and
approximated data. These were obtained by interpolation of, or calculation
from, measured data. This living data update documents the GLODAPv2.2020
methods and provides a broad overview of the secondary quality control
procedures and results.