June 2025

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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

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