in ocean salinity and temperature, which affect density).
However, because capturing these observations required
research vessels, pre-Argo T/S data sets could not attain
systematic global coverage. This changed in the 1990s
with the development of autonomous profiling floats that
enable high-quality T/S observations anywhere at any
time. The Argo Program was designed as a global auton-
omous array of over 3,000 profiling floats spread evenly
over the ocean where the depth exceeds 2,000 m, and it
achieved this milestone in 2007. Free-drifting Argo floats
obtain T/S profiles from 2,000 m depth to the sea surface
every 10 days. All Argo data are distributed freely in near-
real time (12–24 hours) and as research-quality delayed-
mode data (nominally in 12 months). The transformation
in ocean observing brought about by Argo, from exceed-
ingly sparse and regionally biased coverage to systematic
and sustainable global coverage, is apparent in Figure 1.
The combination of Argo and GO-SHIP provides today’s
global observations of the ocean’s interior. GO-SHIP sup-
plies the highest quality global-scale multi-parameter
observations, including biogeochemical as well as physi-
cal properties, from the surface to the seafloor, repeated
on decadal timescales. The accuracy of shipboard data
makes it essential for climate change assessment, sensor
development, and detection and adjustment of drift in
Argo sensors (Sloyan et al., 2019). Additionally, GO-SHIP
provides a scientific foundation for expanding Argo into
full-depth measurements and for investigating the ocean’s
biological and biogeochemical cycling (see next section
on GO-SHIP). In turn, Argo’s systematic, autonomous
sampling provides regional-to-global and seasonal-to-
interannual coverage of T/S that are unattainable by con-
ventional ship-based systems.
Argo has achieved and sustained global observa-
tions because: (1) it provides great value in basic ocean
research, climate variability and change, education, and
ocean forecasting (Johnson et al., 2022); (2) it is based on
effective and efficient global technologies; and (3) it com-
bines with GO-SHIP to provide an ocean observing sys-
tem with unprecedented accuracy and coverage. Central
to Argo’s and GO-SHIP’s successes are their multinational
partnerships composed of academic and government
researchers, agencies charged with ocean observing,
institutions having global reach, and technically proficient
commercial partners.
The transformation of ocean observing brought about
by Argo and GO-SHIP is not complete. GO-SHIP is expand-
ing to include ocean mixing measurements and biological
observations. Deep Argo floats with 6,000 m capability are
increasing Argo’s reach to nearly all the ocean volume,
filling key gaps in our understanding of full-depth ocean
circulation and heat uptake and their relationships with cli-
mate. New sensors for dissolved oxygen, pH, nitrate, and
bio-optical properties have given rise to Biogeochemical
(BGC)-Argo. Core Argo floats are being made more robust,
long-lived, and versatile, enhancing Argo’s coverage, its
sustainability, and the breadth of its applications. The inte-
grated program of Core, Deep, and BGC-Argo (Figure 2),
termed OneArgo, will continue the Argo revolution for sci-
ence and society (Roemmich et al., 2019).
FIGURE 2. The OneArgo array design with floats color-coded for Core, Deep, and Biogeochemical (BGC) Argo. The floats are
randomly distributed in regions with the intention to locate either one or two floats per 3° × 3° square. Courtesy of OceanOPS
60°N
30°N
0°
30°S
60°S
60°E
90°E
120°E
150°E
180°
150°W
120°W
90°W
60°W
30°W
0°
Core Floats (2,500)
Deep Floats (1,200)
BGC Floats (1,000)
OneArgo Design: 4,700 Floats