DEEP ARGO – OBSERVING THE FULL
OCEAN VOLUME
Sustained measurements of ocean properties and circu-
lation are needed over the full water column to provide
fundamental insights into the spatial and temporal extent
of deep ocean warming, sea level rise resulting from the
expanded volume of deep ocean warming, and environ-
mental changes that affect the growth and reproduction
of deep-sea species. Deep ocean (>2,000 m) observing is
sparse in space and time compared to the upper 2,000 m.
Less than 10% of historical non-Argo T/S profiles extend
to depths greater than 2,000 m, with current high-quality
deep ocean measurements limited primarily to GO-SHIP
transects repeated on decadal timescales, ocean stations
located in special regions, and moored arrays set mainly
near the coasts of continents.
To address the void in deep ocean observing, new Deep
Argo float models are designed with high pressure toler-
ance in order to extend autonomous ocean observing to
the abyss. New Deep Argo CTD sensors have improved
temperature, salinity, and pressure accuracies and stability
to resolve deep ocean signals. Use of a bottom-detection
algorithm and bottom-detecting wires enables collection
of temperature, salinity, oxygen, and pressure to as close
as 1–3 m above the seafloor. The implementation of an
ice-avoiding algorithm on all Deep Argo floats deployed at
high latitudes enables deep ocean profiling under sea ice.
The Deep Argo fleet presently consists of pilot arrays
implemented in deep regions where GO-SHIP data show
strong ocean warming (Figure 7). Active float models
include those capable of sampling from the surface to
6,000 m depth, and others that can profile to 4,000 m
(Figure 8). Observations from the pilot arrays show float life-
times reaching 5.5 years and sensor accuracies approach-
ing GO-SHIP quality standards. Deep Argo’s ability is well
demonstrated to measure variability of deep ocean warm-
ing and large-scale deep ocean circulation, both regionally
and globally, at intraseasonal to decadal timescales. The
international Deep Argo community is committed to imple-
menting a global Deep Argo array of 1,250 floats in the next
five to eight years and to sustain Deep Argo observations in
the future (Zilberman et al., 2019).
With full implementation of the Deep Argo array, the
temporal and spatial resolution of deep ocean observa-
tions will improve by orders of magnitude, enabling new
insight into how the deep ocean responds to, distributes,
or influences signals of Earth’s changing climate. Deep
Argo’s homogeneous coverage of the full ocean volume
in all seasons will be particularly useful to constrain and
increase signal-to-error ratios in global ocean reanalyses
and to prevent unrealistic drift in coupled climate-ocean
models. Deep Argo will therefore increase our ability to
predict climate variability and change and to anticipate
and reduce the impact of more frequent extreme weather
events, warmer ocean temperatures, and sea level rise.
These all have damaging implications for various sectors
of the blue economy that nations increasingly depend
upon. Low-lying coastal communities and small island
developing states are especially vulnerable.
FIGURE 8. (a) Deployment of a 4,000 m capable
Deep Arvor float in the North Atlantic Ocean. Photo
courtesy of IFREMER/GEOVIDE (b) Deployment of
a 6,000 m capable Deep SOLO float in the North
Pacific Ocean. Photo credit: Richard Walsh
FIGURE 7. Location of the 191 Deep Argo floats active in October 2021,
including 4,000 m capable Deep Arvor and Deep NINJA, and 6,000 m
capable Deep SOLO and Deep APEX floats. The background colors indi-
cate ocean bottom depth: <2,000 m (white), 2,000–3,000 m (light gray),
3,000–4,000 m (light blue), 4,000–5,000 m (blue), and >5,000 m (dark
gray). Data courtesy of OceanOPS
SIO Deep SOLO (64)
MRV DSeep SOLO (38)
Deep Arvor (60)
Deep NINJA (1)
Deep APEX (28)
60°N
30°N
0°
30°S
60°S
60°E
120°E
180°
120°W
60°W
0°