June 2025 | Oceanography
17
estimated in real time. This four-mooring array also monitors
the background bathymetrically modified circulation that con
trols the mixing and dispersal of the chemical-laden hydrother
mal plume (Xu et al., 2013; Coogan et al., 2017; Figure 3), and
enables researchers to relate circulation dynamics to ecosystem
dynamics (Cuvelier et al., 2014; Lelièvre et al., 2017).
A specialized sonar was developed to image rising plumes
in real time after researchers observed that avoidance sonar on
submersibles could detect reflections from these plumes (Bemis
et al., 2015). The deployment of the Cabled Observatory Vent
Imaging System (COVIS; Figure 4) marked a significant tech
nological milestone. COVIS allows for direct tidal-frequency
resolution of the total flux from the multiple hot vent orifices
that makes up the rising buoyant plume. Utilizing the imagery
of the acoustic backscatter off the turbulent fluctuations of the
buoyant plume and the Doppler shift of the backscattered sig
nal, researchers were able to estimate the rising plume veloc
ity and the expansion rate and heat flux to the ocean from the
hydrothermal venting and its variability through time, and to
gain insights into the diffuse low temperature flow (Bemis et al.,
2012; Xu et al., 2013, 2014).
Chemical analysis of hot vent fluid samples collected by a
remotely controlled, internet-connected serial gas tight sampler
revealed details of the input of nutrient transition metals (e.g., V,
Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo) from the oceanic crust to the
water column (Evans et al., 2023). These metals play an import
ant role in nutrient-related biological processes. They are essen
tial for the growth of organisms and can be rapidly utilized in
near-surface waters and therefore limit growth. Determining
the dynamics of chemical flux across the seafloor interface using
these types of cabled seafloor samplers informs understanding of
the benthic-pelagic coupling that regulates the trophodynamics
over regional scales and offers insights into the global role of
hydrothermal venting in primary and secondary productivity in
the ocean (e.g., Burd and Thomson, 2015; Cathalot et al., 2021).
SOUNDSCAPE
A significant challenge when monitoring a site like Endeavour
is posed by the aggressive environment that can deteriorate
instrumentation quickly, especially when placed in the vicinity
of the plume. Passive acoustic monitoring (PAM) from hydro
phones positioned at a safe distance from the hot and chemically
FIGURE 4. Artist’s rendering
of a selection of ONC’s cabled
and autonomous instruments
monitoring Endeavour. Image
credit: ONC
a. Regional circulation
mooring
b. Junction box
c. Bottom pressure recorder
d. Hydrophone array
e. Broadband seismometer
f. Cabled Observatory Vent
Imaging Sonar
g. Passive larval trap collector
h. Sediment trap
i. Deep Acoustic Lander
j. Remotely operated vehicle
k. Water sampler
l. TEMPO-Mini ecological
module
m. Benthic and Resistivity
Sensors
June 2025 | Oceanography
17