Oceanography | Early Online Release
calculus. Low-resolution, surface-vessel-based maps can now be
used to guide higher-resolution AUV-based surveys. AUVs can
run in close proximity to the ground compared to a vessel at the
sea surface, thus providing much more detail on what lies below.
The combination of nested surface vessel-AUV-ROV surveys has
greatly aided our understanding of underwater landscapes and
how they evolve, and this approach now informs choices on what
locations to observe more closely and repeatedly to improve the
odds of making new discoveries (e.g., Caress et al., 2008, 2012;
Paull et al., 2010; Paduan et al., 2018, Figure 8).
Even highly detailed bathymetric surveys fail to reveal much
about the animals that inhabit the seafloor. With relatively few
exceptions, most life on the seabed is sub-meter scaled and often
transparent to acoustic energy. By combining high-resolution laser
and optical imagery with acoustic mapping, a truly astounding
view of the seafloor emerges (Figure 9). The systems for acquir
ing that information can be deployed on ROVs (e.g., Caress et al.,
2025) and are extendable to AUVs, greatly expanding the area that
can be surveyed in detail. Processing the imagery collected using
machine learning techniques also holds promise for significantly
speeding up quantitative assessments of specific animals or other
features of interest even while the vehicle is underway. Further
study of the famed octopus garden provides a stunning example of
what is possible when combining different modes of seafloor visu
alizations to inform targeted studies that not long ago would have
seemed a pipe dream (Barry et al., 2023; Figure 9). Similar studies
of deep-sea coral and sponge communities found serendipitously
at Sur Ridge and elsewhere paint a similar picture (Girard et al.,
2024; Figure 10). These discoveries highlight what is made pos
sible by using a combination of hybrid human-machine and fully
autonomous systems for visualizing the seafloor.
Despite that progress, the vast majority of the seabed has never
been mapped at scales needed to reveal underwater landscapes
in detail. Satellite altimetry-derived maps provide ~5 km grid
resolution estimates of seafloor depth for the entire ocean bottom
using gravity anomalies (W.H.F. Smith and Sandwell, 1997), but
those maps provide only a coarse perspective on what lies below,
much like a person viewing a large terrestrial mountain range, deep
valley, or vast plain from a great distance. High-resolution maps
of the seafloor acquired using surface vessel-mounted multibeam
sonar varies linearly with water column depth, typically on the order
of 2 m at 100 m depth to 100 m at 5,000 m depth (Mayer, 2006), but
even those maps currently cover only ~26% of the ocean bottom.
Visualizing deep-sea biological communities requires much higher
resolution, ideally centimeter or even millimeter scale, as shown in
Figure 9. In other words, much of what lies below has never been
seen by human eyes. Although the technology for doing so is avail
able, actually accomplishing that goal globally is an enormous task
and not likely to come to fruition anytime soon. Once again, robots
offer a path forward for tackling that challenge because they can
work when and where people cannot, dare not, or just prefer to
avoid for many practical and logistical reasons.
A combination of crewed and uncrewed surface and subsurface
vessels are now actively engaged in mapping the entirety of the sea
floor as a contribution to the Seabed 2030 initiative. Seabed 2030 is
a collaborative project sponsored by the Nippon Foundation and
the General Bathymetric Chart of the Ocean (GEBCO) that aims to
assemble all available bathymetric data into a single, freely accessi
ble map for the benefit of all. Like the global fleet of profiling floats
returning data on the vital signs of the world’s ocean, Seabed 2030
is a great example of what can be accomplished through public-
private partnerships, international cooperation, and data sharing to
grow our understanding of seafloor bathymetry. Given the task at
hand and its relevance to society, it speaks to the age-old adage that
“necessity is the mother of invention.” Developing new means for
comprehensively mapping the seafloor is ripe for innovation, fol
lowing in the footsteps of developing and deploying platforms and
sensors for assessing ocean biogeochemistry on a global scale.
FIGURE 8. Animation demon
strates the combined use of ship,
AUV, and ROV-based surveys to
obtain
high-resolution
seafloor
bathymetry and imagery at Sur
Ridge within the Monterey Bay
National Marine Sanctuary (Seeing
Sur Ridge). © 2023 MBARI