CORE ARGO – SUSTAINING AND IMPROVING
SYSTEMATIC GLOBAL OCEAN OBSERVATIONS
FOR CLIMATE
The highest priority for the OneArgo Program is to sus-
tain and improve the longstanding Core Argo array
(Figure 5). The sustainability of an observing system
depends equally on the societal needs driving it and on its
cost- effectiveness. Core Argo’s primary roles are in assess-
ments of global warming, sea level rise, and the hydro-
logical cycle, plus applications in seasonal- to- interannual
ocean and coupled forecasting, and ocean state estimation.
Other research topics that utilize Argo data include ocean
circulation in interior and boundary current regions, meso-
scale eddies, ocean mixing, marine heatwaves, water mass
properties and formation, El Niño-Southern Oscillation,
and ocean dynamics. Argo’s rapidly growing applications
are well documented (e.g., Johnson et al., 2022), with about
500 research papers that use Argo data published per year.
While the scientific needs for Core Argo are strong,
equally important are the technology advancements
in profiling floats and sensors that are transforming
the cost- effectiveness of the array while enabling new
scientific missions.
• Float engineering: Advances in the hydraulic system
controlling float buoyancy have contributed to sub-
stantial decreases in float failure rates (Figure 6) while
increasing energy efficiency for longer float missions.
• Battery technology: The use of improved (hybrid) lith-
ium batteries since about 2016 is doubling the battery
lifetime of some Core Argo float models from about five
years to 10 years.
• Satellite communications: Around 2011, Argo com-
munications transitioned from the one-way System
ARGOS to the bidirectional Iridium global cellular net-
work. A float’s time on the sea surface for data trans-
mission was reduced from 10 hours to 15 minutes in
each cycle, resulting in energy savings and avoidance
of surface hazards, including grounding and biofoul-
ing. New applications have emerged utilizing the rapid
data turnaround, while the bidirectional transmissions
enable changes in mission parameters throughout
float lifetimes.
In the transition to OneArgo, Core Argo coverage require-
ments (Figure 2) are increasing in key regions. Doubling
of float density in the equatorial Pacific is needed by the
Tropical Pacific Observing System (https://tpos2020.org).
Similarly, doubling is needed in western boundary regions
that exhibit high variability and in marginal seas adjacent
to the continental shelves. Increasing coverage in high-
latitude, seasonally ice-covered regions is accomplished
by using T/S to infer ice-free conditions and by using
ice-hardened antennas. The map of OneArgo coverage
(Figure 2) shows that expanded coverage of 0–2,000 m
T/S profiles will be accomplished even as the number of
exclusively Core Argo floats decreases, because Deep and
BGC Argo floats also collect 0–2,000 m (Core) T/S profiles.
Core Argo will continue the technology and scientific rev-
olutions that have transformed global observing from a
vision to reality.
FIGURE 5. Locations of active Argo floats, including those for the Core, Deep, and Biogeochemical
(BGC) programs, color-coded by national program, as of July 2021. Courtesy of OceanOPS
90°N
60°N
30°N
0°
30°S
60°S
90°S
60°E
90°E
120°E
150°E
180°
150°W
120°W
90°W
60°W
30°W
0°
Argo National Contributions: 3,894 Floats
FIGURE 6. Survival rates (%) of US Argo
floats (dashed lines) and all Argo floats
(solid lines) over an initial five-year period
for those deployed in 2015 (blue) com-
pared with those deployed in Argo’s first
five years (2000–2004, red). Data cour-
tesy of OceanOPS
100
80
60
40
20
Survival Rate (%)
Year
Argo Survival Rate by Deployment Year
2000–2004
2015
Solid Lines = All Argo
Dashed Lines = US Argo
0
1
2
3
4