Oceanography
THE OFFICIAL MAGAZINE OF THE OCEANOGRAPHY SOCIETY
VOL. 38, NO. 2, JUNE 2025
Video of a thin black smoker chimney spire, part of the Godzilla/Bambi complex in the northern part of the
High Rise Vent Field on Endeavour Ridge, Northeast Pacific Ocean. Jump to page 10 to read the full article
by Mihály et al. Video courtesy of Ocean Networks Canada
June 2025 | Oceanography
10
40
24
36
3 QUARTERDECK. What Do Cuts to US Science Mean for Oceanography
By E.S. Kappel
5 PERSPECTIVE. Setting a Course for Research on Offshore Wind
Development Impacts Near Nantucket Shoals
By G. Gawarkiewicz
7 PERSPECTIVE. Zooplankton and Offshore Wind: Drifters in a Sea
of Uncertainty
By G.K. Saba
10 FEATURE ARTICLE. Scientific Research and Marine Protected
Area Monitoring Using a Deep-Sea Observatory: The Endeavour
Hydrothermal Vents
By S.F. Mihály, F.C. De Leo, E. Minicola, L. Muzi, M. Heesemann, K. Moran,
and J. Hutchinson
24 FEATURE ARTICLE. How Do Tides Affect Underwater Acoustic Propagation?
A Collaborative Approach to Improve Internal Wave Modeling at Basin to
Global Scales
By M.C. Schönau, L. Hiron, J. Ragland, K.J. Raja, J. Skitka, M.S. Solano, X. Xu,
B.K. Arbic, M.C. Buijsman, E.P. Chassignet, E. Coelho, R.W. Helber, W. Peria, J.F. Shriver,
J.E. Summers, K.L. Verlinden, and A.J. Wallcraft
36 FEATURE ARTICLE. From Wind to Whales: Potential Hydrodynamic Impacts
of Offshore Wind Energy on Nantucket Shoals Regional Ecology
By E.E. Hofmann, J.R. Carpenter, Q.J. Chen, J.T. Kohut, R.L. Merrick, E.L. Meyer-Gutbrod,
D.P. Nowacek, K. Raghukumar, N.R. Record, and K. Oskvig
40 FEATURE ARTICLE. Overview of the Atlantic Deepwater Ecosystem
Observatory Network
By J.L. Miksis-Olds, M.A. Ainslie, H.B. Blair, T. Butkiewicz, E.L. Hazen, K.D. Heaney,
A.P. Lyons, B.S. Martin, and J.D. Warren
52 FEATURE ARTICLE. Exploring Climate Change, Geopolitics, Marine
Archeology, and Ecology in the Arctic Ocean Through Wood-Boring Bivalves
By J. Berge, T. Bakken, K. Heggland, J.-A. Sneli, Ø. Ødegård, M. Ingulstad, T. Thun,
and G. Johnsen
contents VOL. 38, NO. 2, JUNE 2025
June 2025 | Oceanography
Oceanography | Vol. 38, No. 2
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58 MEETING REPORT. Community Recommendations on Belonging,
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66 DIY OCEANOGRAPHY. The PIXIE: A Low-Cost, Open-Source, Multichannel
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86 BOOK REVIEW. A Philosophical View of the Ocean and Humanity, Second
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88 CAREER PROFILES. Lilian (Lica) Krug, Scientific Coordinator, Partnership
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66
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ON THE COVER
A thin black smoker chimney spire,
part of the Godzilla/Bambi complex in
the northern part of the High Rise Vent
Field on Endeavour Ridge, Northeast
Pacific Ocean. Video courtesy of
Ocean Networks Canada
Oceanography | Vol. 38, No. 2
June 2025 | Oceanography
A lot has already been published about the how the current and
anticipated steep reductions in US federal funding for science,
along with reductions in staffing at federal agencies, will affect
the scientific enterprise, though not all the collateral damage has
been picked up in news stories nor assessed (e.g., Flannery, 2025;
Garisto, 2025; Harvey, 2025; Wadman, 2025). From my perch,
as editor of Oceanography, I’ve been thinking about what fed
eral funding cuts might mean for scientific publishing, and for
this journal in particular. For decades, US federal agency sup
port has been vital to the long-term health of Oceanography
and our ability to openly share critical research on a wide vari
ety of ocean science related topics. Many special issues and indi
vidual articles have been used as a basis for undergraduate and
graduate classroom instruction and discussions as well as to
inform policymakers.
Federal support has also enabled us to publish two special
issues on Women in Oceanography and more recently a special
issue on Building Diversity, Equity, and Inclusion in the Ocean
Sciences. Three federal agencies supported this year’s special
issue on A Vision for Capacity Sharing in the Ocean Sciences.
These landmark special issues are contributing in various ways
to inspiring the careers of our next generation of ocean scientists,
who are vital to the continued health of our field. Importantly,
special issue sponsorship means that no authors pay publication
fees, allowing scientists from under-resourced nations or others
who may not have large research grants to fully participate. This
sponsorship also enabled The Oceanography Society (TOS), the
publisher of Oceanography and a nonprofit organization, to pro
vide full open access to articles long before it was fashionable, or
even required, for scientific journals.
From the beginning, Oceanography’s mission has been to
communicate across disciplines in the ocean sciences—a dif
ferent but complementary objective from other, more techni
cal journals in our field. The aspiration is that special issues and
individual articles that are accessible to all ocean scientists, and
contributed by the global community, may spur new collabora
tions or provide new insights that will advance the field. While
Oceanography will continue to pursue its mission by publish
ing special issues as the situation permits, there will likely be
fewer in the future unless sponsorship opportunities with other
US-based organizations as well as groups outside of the United
States arise. Instead, we will publish more “regular” (unspon
sored) issues that are based on unsolicited manuscripts (e.g., this
June 2025 issue; see also the September 2024 issue).
I highly encourage TOS members to check out our Author
Guidelines for instructions on how to submit a manuscript
to Oceanography and to share those guidelines with your col
leagues. If you are unsure whether a topic might be of interest to
us, please contact one of the associate editors and discuss your
idea. Your articles, whether published in a regular or special
issue, are vital to communication among ocean scientists and
the continued health of Oceanography.
WHAT DO CUTS TO US SCIENCE
MEAN FOR OCEANOGRAPHY?
Ellen S. Kappel, Editor
REFERENCES
Flannery, M.E. 2025. “Scientific Research is Getting Cut—And That Should Scare All Americans.” neaToday, March 5, 2025, https://www.nea.org/nea-today/all-news-articles/
scientific-research-getting-cut-and-should-scare-all-americans.
Garisto, D. 2025. “Trump Moves To Slash NSF: Why Are the Proposed Budget Cuts So Big?” Nature, June 5, 2025, https://doi.org/10.1038/d41586-025-01749-x.
Harvey, C., 2025. “Trump Takes a Giant ‘Wrecking Ball’ to US Research.” E&E News, February 18, 2025, https://www.eenews.net/articles/trump-takes-giant-wrecking-
ball-to-us-research/.
Wadman, M. 2025. “National Academies, Staggering From Trump Cuts, on Brink of Dramatic Downsizing.” Science, June 2, 2025, https://doi.org/10.1126/science.z4wjf7q.
ARTICLE DOI. https://doi.org/10.5670/oceanog.2025.313
QUARTERDECK
Oceanography | Vol. 38, No. 2
September 2024 | Oceanography
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June 2025 | Oceanography
PERSPECTIVE
The National Academies Consensus Study Report, Potential
Hydrodynamic Impacts of Offshore Wind Energy on Nantucket
Shoals Regional Ecology: An Evaluation from Wind to Whales
(NASEM, 2024), is important, timely, and succinct. During this
time of political and financial uncertainty regarding the devel
opment of offshore wind, this report, summarized by Hofmann
et al. (2025, in this issue), offers clear directions for the research
needed to resolve significant scientific and engineering questions
during a time of rapid change in the Northwest Atlantic Ocean.
The report highlights the difficulty of unraveling the impacts
of offshore wind development from oceanographic variabil
ity. The Northwest Atlantic is one of the most rapidly warm
ing regions in the world ocean (e.g., Pershing et al., 2015; Chen
et al., 2020; Seidov et al., 2021), resulting in a trend of increas
ing stratification in the region (Harden et al., 2020). While
there is a longer-term warming trend, in part relating to vari
ability upstream (e.g., Gonçalves Neto et al., 2021), extreme
events, such as marine heatwaves in the region, have resulted
in large temperature anomalies over time periods from days
to months. Further complicating the matter, the spatial scales
of the marine heatwaves depend on whether they result from
atmospheric forcing or ocean advection (e.g., Chen et al., 2014;
Großelindemann et al., 2022).
Another factor that makes attributing impacts in the region
complex is the manner in which Gulf Stream variability has influ
enced continental shelf stratification and water mass properties
via increases in shelf break exchange processes. Gulf Stream
meanders have increased in peak-to-trough size, and their first
downstream appearance from the Cape Hatteras destabilization
point first shifted west over an extended period of time (Andres,
2016) and then shifted eastward over the last several years
(Sánchez-Roman et al., 2024). This increased Gulf Stream vari
ability is likely related to a regime shift in the annual formation
rate of warm core rings in the year 2000 (Gangopadhyay et al.,
2019). An indication of the growing influence of Gulf Stream
rings and water masses on the continental shelf in this region
is the remarkable increase in frequency of mid-depth salinity
maximum intrusions (Gawarkiewicz et al., 2022). These intru
sions commonly occur in proximity to warm core rings (Silver
et al., 2023) and bring warm salty water tens of kilometers shore
ward of the shelf break and potentially into the offshore wind
lease areas off Nantucket Shoals. Significantly for northern right
whale prey fields, salinity profiles reveal there may be several dif
ferent intrusions at different depths in the water column over the
continental shelf, thus possibly diminishing the concentration
within an individual intrusion layer.
The flow around offshore wind turbines is affected by pre-
existing continental shelf processes and in turn alters those pro
cesses. A key contribution of the Consensus Study Report is to
clearly delineate the three major scales over which the effects
on hydrodynamics must be considered and assessed: the indi
vidual turbine scale, the wind farm scale including all turbines
in the region, and the larger regional scale over which the wind
farm scale exerts an impact via advection and changes in stratifi
cation. This delineation is important as both the computational
approaches and the observational tools differ among the differ
ent spatial scales. Prioritization is important, as is the linkage in
understanding among the scales.
A key portion of the report is the careful evaluation and sum
mary of numerical modeling studies that highlight the wide
uncertainties regarding the impacts of turbine wakes on strati
fication. Most of these studies have been directed toward infra
structure in the North Sea, which exhibits considerable dif
ferences in stratification, tidal velocities, and wind forcing
relative to the Nantucket Shoals region. Validation of mod
els with careful observations is stressed and will be crucial to
reducing uncertainties.
Several challenges inhibit progress over these three spatial
scales. Large Eddy Simulations are needed at the individual tur
bine scale to parameterize mixing and the downstream evo
lution of turbulent wakes from the turbines. On larger scales,
much of the small-scale turbulence will need to be parameter
ized. Progress in this specific area has been achieved by numer
ical modelers in Europe, and parallel efforts are needed for the
Nantucket Shoals region.
A significant gap that is not addressed directly in the report is
the manner in which internal waves and tides have been chang
ing over the past decade as stratification has changed. In addition
SETTING A COURSE
FOR RESEARCH ON OFFSHORE WIND DEVELOPMENT
IMPACTS NEAR NANTUCKET SHOALS
By Glen Gawarkiewicz
Oceanography | Vol. 38, No. 2
to ambient mesoscale and submesoscale processes, the charac
teristics of the high frequency processes have likely changed
even in the absence of the wind farms. Again, it will be a chal
lenge to differentiate changes resulting from the offshore wind
development and those that may have occurred as a result of
changing ocean currents and stratification. There is a clear need
for observations focused on high frequency processes to support
the numerical modeling.
All of the knowledge generated in understanding hydro
dynamic effects will also need to be applied to further under
standing regional marine ecology, as the prey fields, including
prey aggregation, and the roles of convergences and localized
upwelling in generating observed prey concentrations must be
better understood.
There are many challenges ahead, but the Consensus Study
Report produced by this NASEM committee is the clearest state
ment possible of the path forward. This is particularly import
ant, as the varied funding entities include federal agencies, off
shore wind developers, and foundations for all of which this
report provides clear guidance on research needs and directions.
Given the dire need for alternative energy sources, there is an
urgent need for progress. The committee should be commended
for producing a clear, eminently readable report with strong rec
ommendations. Let us hope that the resources become available
to meet the challenges that they so eloquently describe.
REFERENCES
Andres, M. 2016. On the recent destabilization of the Gulf Stream path down
stream of Cape Hatteras. Geophysical Research Letters 43(18):9,836–9,842,
https://doi.org/10.1002/2016GL069966.
Chen, K., G.G. Gawarkiewicz, S.J. Lentz, and J.M. Bane. 2014. Diagnosing the
warming of the Northeastern US Coastal Ocean in 2012: A linkage between the
atmospheric jet stream variability and ocean response. Journal of Geophysical
Research: Oceans 119(1):218–227, https://doi.org/10.1002/2013JC009393.
Chen, Z., Y.O. Kwon, K. Chen, P. Fratantoni, G. Gawarkiewicz, and T.M. Joyce.
2020. Long-term SST variability on the Northwest Atlantic continental shelf and
slope. Geophysical Research Letters 47(1):e2019GL085455, https://doi.org/
10.1029/2019GL085455.
Gangopadhyay, A., G. Gawarkiewicz, E.N.S. Silva, M. Monim, and J. Clark. 2019. An
observed regime shift in the formation of warm core rings from the Gulf Stream.
Scientific Reports 9(1):12319, https://doi.org/10.1038/s41598-019-48661-9.
Gawarkiewicz, G., P. Fratantoni, F. Bahr, and A. Ellertson. 2022. Increasing fre
quency of mid depth salinity maximum intrusions in the Middle Atlantic Bight.
Journal of Geophysical Research: Oceans 127:e2021JC018233, https://doi.org/
10.1029/2021JC018233.
Gonçalves Neto, A., J.A. Langan, and J.B. Palter. 2021. Changes in the Gulf Stream
preceded rapid warming of the Northwest Atlantic Shelf. Communications Earth
& Environment 2(1):74, https://doi.org/10.1038/s43247-021-00143-5.
Großelindemann, H., S. Ryan, C.C. Ummenhofer, T. Martin, and A. Biastoch. 2022.
Marine heatwaves and their depth structures on the northeast US continental
shelf. Frontiers in Climate 4:857937, https://doi.org/10.3389/fclim.2022.857937.
Harden, B.E., G.G. Gawarkiewicz, and M. Infante. 2020. Trends in physical proper
ties at the southern New England shelf break. Journal of Geophysical Research:
Oceans 125(2):e2019JC015784, https://doi.org/10.1029/2019JC015784.
Hofmann, E.E., J.R. Carpenter, Q.J. Chen, J.T. Kohut, R.L. Merrick, E.L. Meyer-
Gutbrod, D.P. Nowacek, K. Raghukumar, N.R. Record, and K. Oskvig. 2025. From
wind to whales: Potential hydrodynamic impacts of offshore wind energy on
Nantucket Shoals regional ecology. Oceanography 38(2):36–39, https://doi.org/
10.5670/oceanog.2025.304.
NASEM (National Academies of Sciences, Engineering, and Medicine). 2024.
Potential Hydrodynamic Impacts of Offshore Wind Energy on Nantucket Shoals
Regional Ecology: An Evaluation from Wind to Whales. The National Academies
Press, Washington, DC, https://doi.org/10.17226/27154.
Pershing, A.J., M.A. Alexander, C.M. Hernandez, L.A. Kerr, A. Le Bris, K.E. Mills,
J.A. Nye, N.R. Record, H.A. Scannell, J.D. Scott, and G.D. Sherwood. 2015. Slow
adaptation in the face of rapid warming leads to collapse of the Gulf of Maine
cod fishery. Science 350(6262):809–812, https://doi.org/10.1126/science.aac9819.
Sánchez-Román, A., F. Gues, R. Bourdalle-Badie, M.I. Pujol, A. Pascual, and
M. Drévillon. 2024. Changes in the Gulf Stream path over the last 3 decades.
In Copernicus Ocean State Report, 8th ed. K. von Schuckmann, L. Moreira,
M. Grégoire, M. Marcos, J. Staneva, P. Brasseur, G. Garric, P. Lionello,
J. Karstensen, and G. Neukermans, eds, Copernicus Publications, 4-osr8,
https://doi.org/10.5194/sp-4-osr8-4-2024.
Seidov, D., A. Mishonov, and R. Parsons. 2021. Recent warming and
decadal variability of Gulf of Maine and Slope Water. Limnology and
Oceanography 66(9):3,472–3,488, https://doi.org/10.1002/lno.11892.
Silver, A., A. Gangopadhyay, G. Gawarkiewicz, P. Fratantoni, and J. Clark. 2023.
Increased gulf stream warm core ring formations contributes to an observed
increase in salinity maximum intrusions on the Northeast Shelf. Scientific
Reports 13(1):7538, https://doi.org/10.1038/s41598-023-34494-0.
AUTHOR
Glen Gawarkiewicz (ggawarkiewicz@whoi.edu), Woods Hole Oceanographic
Institution, Woods Hole, MA, USA.
ARTICLE CITATION
Gawarkiewicz, G. 2025. Setting a course for research on offshore wind develop
ment impacts near Nantucket Shoals. Oceanography 38(2):5–6, https://doi.org/
10.5670/oceanog.2025.303.
COPYRIGHT & USAGE
This is an open access article made available under the terms of the Creative
Commons Attribution 4.0 International License (https://creativecommons.org/
licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and repro
duction in any medium or format as long as users cite the materials appropriately,
provide a link to the Creative Commons license, and indicate the changes that
were made to the original content.
June 2025 | Oceanography
ZOOPLANKTON AND OFFSHORE WIND
DRIFTERS IN A SEA OF UNCERTAINTY
By Grace K. Saba
Scientists are often tasked with addressing challenging, seem
ingly impossible questions. An example is the recent Consensus
Study Report (NASEM, 2024a)—summarized by Hoffman
et al. (2025, in this issue)—asking: “How will potential offshore
wind-induced changes in ocean physical dynamics affect the
North Atlantic right whale in the Nantucket Shoals region?”
Most concerns about potential direct impacts of offshore wind
farms (OSW) on the North Atlantic right whale (NARW) focus
on noise interference and higher vessel activity increasing the
risk of vessel strikes. The impact of OSW on ocean physics or
hydrodynamics and subsequently NARWs is more difficult to
gauge because the effects are indirect and likely highly vari
able. We do not yet know enough to accurately predict when
and where zooplankton will aggregate at concentrations that
support NARW foraging and success. Additionally, the under
lying confounding challenge is how to decipher turbine-induced
hydrodynamic changes relative to the background of extremely
high spatiotemporal variability in oceanographic conditions and
zooplankton dynamics in the Nantucket Shoals region. When
posed as a modified question—“How will potential OSW-
induced changes in ocean physical dynamics affect zooplankton
in the Nantucket Shoals region?”—a variety of scenarios come
to mind along with three questions that need to be addressed in
order to move closer to understanding whether and how OSW
may impact zooplankton.
WHAT CONTROLS ZOOPLANKTON SUPPLY AND
THE FORMATION OF AGGREGATIONS AT LEVELS
SUFFICIENT FOR NARW FEEDING?
The number of NARWs in the Nantucket Shoals region has
increased over the past decade, and although their peak for
aging occurs during the winter and spring seasons, their pres
ence has been observed year-round (Quintana-Rizzo et al.,
2021). Successful NARW foraging requires an adequate sup
ply and concentration of zooplankton (103–104 individuals m–3;
Baumgartner and Mate, 2003) as well as mechanisms that pro
duce high-density aggregations at 100–1,000 m spatial scales
(Sorochan et al., 2021), which coincidentally match those of
potential single turbine impacts. Coastal currents from the
Gulf of Maine and the Great South Channel control the supply
of NARWs’ primary prey, late stages of Calanus finmarchicus,
to Nantucket Shoals, while alternative copepod prey species
(Centropages spp., Pseudocalanus spp. Paracalanus spp., Oithona
similis) occur year-round with relatively different times of peak
abundance (Sorochan et al., 2021). We do not yet fully under
stand the specific mechanism(s) that facilitate the production of
high-density zooplankton layers and aggregations in and around
Nantucket Shoals, as simultaneous NARW sightings and cope
pod aggregations have not been observed at either tidal mixing
fronts or in a locally persistent wintertime upwelling gyre (Leiter
et al., 2017; Sorochan et al., 2021). The interactions between
source and advective supply, behavior (e.g., vertical migration),
ontogenetic cycles, food availability and distribution, and ocean
physical conditions that regulate these variables likely influence
zooplankton aggregation in the Nantucket Shoals region. These
dynamics are likely species-specific. Therefore, observational
studies in this region need to focus on determining which prey
species NARWs are targeting and on collecting high-resolution
spatiotemporal observations of concurrent physical oceano
graphic properties, copepod species distributions and aggrega
tion dynamics, and NARW presence.
HOW MIGHT OSW AFFECT ZOOPLANKTON
ABUNDANCE AND AGGREGATION POTENTIAL?
A severe lack of observational data means that we do not know
the potential turbine-induced downstream and surrounding
increased turbulence and wake effects at scales of 0.1–1.0 km.
This could lead to, or alternate between, different scenarios of
OSW acting on zooplankton that are dependent on seasonal
ocean physical structure, circulation patterns, biological pro
cesses, and highly variable wind, current, mixing, and tidal
dynamics. An added layer of complexity is that different zoo
plankton species may respond differently to hydrodynamic
changes due to variable behaviors, preferred food resources,
and seasonal cycles.
Five possible scenarios are outlined here. One scenario is
that there is no overall effect; Figure 1 depicts the remaining
four. Scenario A would act to disperse surface zooplankton
aggregations and potentially those in diapause at depth (Incze
et al., 2001). Whether this scenario could negatively change
PERSPECTIVE
Oceanography | Vol. 38, No. 2
Flow direction
Higher wind speed
Flow direction
Lower wind speed
Wind wake
Higher turbulence & ocean wake
Physical dispersion of zooplankton
(Late fall – Early spring; Unstratified)
*Seasonally
high wind
speeds
Low turbulence & ocean wake
Nutrient injection
Phytoplankton
Flow direction
Higher wind speed
Flow direction
Lower wind speed
Wind wake
Zooplankton
aggregation
Bottom-up support of zooplankton aggregation
(Late spring – Early fall; Strongly stratified)
*Seasonally
low wind
speeds
Flow direction
Higher wind speed
Flow direction
Lower wind speed
Wind wake
Higher turbulence & ocean wake
Physical dispersion of zooplankton
(Mid-spring, Mid-fall; Weakly stratified)
*Seasonally
moderate
wind speeds
Flow direction
Higher wind speed
Flow direction
Lower wind speed
Wind wake
Top-down predation on zooplankton
(All seasons)
*Seasonally
variable
wind speeds
Scenario A
Scenario B
Scenario C
Scenario D
FIGURE 1. Four potential scenarios of offshore wind turbulence and wake effects on
zooplankton in Nantucket Shoals waters.
zooplankton availability and aggregations at a level
that would impact NARW foraging is an open ques
tion. This scenario may be of most relevance to
NARW ecology because it encompasses the time
frame when NARW are most abundant and actively
foraging in Nantucket Shoals waters. In Scenario B,
OSW effects are strong enough to slightly disrupt
stratification, permitting nutrient injection upward
into the surface layer, but not strong enough to
break down stratification and disperse aggregat
ing zooplankton. These higher nutrient conditions
could enhance primary production and therefore
zooplankton (Carpenter et al., 2016; Floeter et al.,
2017). Scenario C would destabilize stratification
(Carpenter et al., 2016; Miles et al., 2017), which
could potentially disperse zooplankton aggrega
tions similarly to Scenario A. However, current
velocities would need to be high enough, and strat
ification weak enough, for OSW-induced turbu
lence to break down stratification (Carpenter et al.,
2016) and negatively impact zooplankton aggrega
tions. Scenario D involves a more biological mecha
nism whereby high colonization and abundances of
filter feeding invertebrates (e.g., mussels) on turbine
structures facilitate a top-down decrease in zoo
plankton abundance (Perry and Heyman, 2020).
Although this scenario is independent of season,
different physical conditions and levels of turbu
lence will create variable encounter rates and inter
action times between sessile predators and zoo
plankton prey (Prairie et al., 2012).
At the wind farm scale (10–100 km), cumula
tive impacts of multiple turbines may act to reduce
surface current speeds and stratification and cre
ate horizontal shear-induced upwelling and down
welling dipoles that could differentially aggregate
or disaggregate zooplankton (Carpenter et al., 2016;
Sorochan et al., 2021; Christiansen et al., 2023).
Evaluating wind farm-scale impacts on oceano
graphic and zooplankton dynamics will be more
difficult to isolate from regional high natural envi
ronmental variability.
ARE THESE POTENTIAL OSW IMPACTS
ON ZOOPLANKTON GREATER
THAN NATURAL PROCESSES
THAT DRIVE A RANGE OF SCALES
OF SPATIOTEMPORAL VARIABILITY?
Oceanographic conditions on Nantucket Shoals
and on the broader US Northeast shelf are sub
ject to high daily to decadal variability, driven
by local wind conditions, tidal forcing, storm
June 2025 | Oceanography
activity, and fluctuations in large-scale circulation (summa
rized in NASEM, 2024a). Furthermore, increased frequency
of mid-water salt intrusions into shelf waters has been associ
ated with recent warming, an inshore movement of the shelf-
break front, and changes in water column structure (Harden
et al., 2020; Gawarkiewicz et al., 2022). Zooplankton abun
dance and distribution follow similar trends of variability, lead
ing to spatiotemporal fluctuations in NARW foraging habitat,
including warming-associated declines in C. finmarchicus and
Pseudocalanus spp. (Record et al., 2019).
Given the significant uncertainty outlined here, the initial
question really should be how do we determine if OSW will
affect zooplankton and NARW in the Nantucket Shoals region?
Luckily, as Hoffman et al. (2025, in this issue) indicate, the com
munity now has some guidance through the recently released
workshop proceedings, Nantucket Shoals Wind Farm Field
Monitoring Program (NASEM, 2024b). Isolating OSW impacts
from natural variability will require monitoring and model
ing studies designed to target specific impacts at relevant scales
with sufficient resolution. Localized field efforts should sam
ple along a gradient inside and outside OSW fields or include
“control” areas outside of OSW areas, before, during, and
after construction. Monitoring should also include simultane
ous physical and biological observations at both the turbine
and wind farm area scale as well as repetition during variable
oceanographic conditions.
REFERENCES
Baumgartner, M.F., and B.R. Mate. 2003. Summertime foraging ecology of
North Atlantic right whales. Marine Ecology Progress Series 264:123–135,
https://doi.org/10.3354/meps264123.
Carpenter, J.R., L. Merckelbach, U. Callies, S. Clark, L. Gaslikova, and B. Baschek.
2016. Potential impacts of offshore wind farms on North Sea stratification.
PLoS ONE 11(8):e0160830, https://doi.org/10.1371/journal.pone.0160830.
Christiansen, N., J.R. Carpenter, U. Daewel, N. Suzuki, and C. Schrum. 2023. The
large-scale impact of anthropogenic mixing by offshore wind turbine foundations
in the shallow North Sea. Frontiers in Marine Science 10:1178330, https://doi.org/
10.3389/fmars.2023.1178330.
Floeter, J., J.E.E. van Beusekom, D. Auch, U. Callies, J. Carpenter, T. Dudeck,
S. Eberle, A. Eckhardt, D. Gloe, K. Hänselmann, and others. 2017. Pelagic effects
of offshore wind farm foundations in the stratified North Sea. Progress in
Oceanography 156:154–173, https://doi.org/10.1016/j.pocean.2017.07.003.
Gawarkiewicz, G., P. Fratantoni, F. Bahr, and A. Ellertson. 2022. Increasing fre
quency of mid-depth salinity maximum intrusions in the Middle Atlantic Bight.
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10.1029/2021JC018233.
Harden, B., G.G. Gawarkiewicz, and M. Infante. 2020. Trends in physical proper
ties at the southern New England shelf break. Journal of Geophysical Research:
Oceans 125(2):e2019JC015784, https://doi.org/10.1029/2019JC015784.
Hofmann, E.E., J.R. Carpenter, Q.J. Chen, J.T. Kohut, R.L. Merrick, E.L. Meyer-
Gutbrod, D.P. Nowacek, K. Raghukumar, N.R. Record, and K. Oskvig. 2025. From
wind to whales: Potential hydrodynamic impacts of offshore wind energy on
Nantucket Shoals regional ecology. Oceanography 38(2):36–39, https://doi.org/
10.5670/oceanog.2025.304.
Incze, L.S., D. Hebert, N. Wolff, N. Oakey, and D. Dye. 2001. Changes in copepod
distributions associated with increased turbulence from wind stress. Marine
Ecology Progress Series 213:229–240, https://doi.org/10.3354/meps213229.
Leiter, S.M., K.M. Stone, J.L. Thompson, C.M. Accardo, B.C. Wikgren, M.A. Zani,
T. Cole, R.D. Kenney, C.A. Mayo, and S.D. Kraus. 2017. North Atlantic
right whale Eubalaena glacialis occurrence in offshore wind energy
areas near Massachusetts and Rhode Island, USA. Endangered Species
Research 34:45–59, https://doi.org/10.3354/esr00827.
Miles, J., T. Martin, and L. Goddard. 2017. Current and wave effects around wind
farm monopile foundations. Coastal Engineering 121:167–178, https://doi.org/
10.1016/j.coastaleng.2017.01.003.
NASEM (National Academies of Science, Engineering, and Medicine). 2024a.
Potential Hydrodynamic Impacts of Offshore Wind Development on Nantucket
Region Ecology: An Evaluation from Wind to Whales. The National Academies
Press, Washington DC, 120 pp., https://doi.org/10.17226/27154.
NASEM. 2024b. Nantucket Shoals Wind Farm Field Monitoring Program.
The National Academies Press, Washington, DC, 64 pp., https://doi.org/
10.17226/28021.
Perry, R.L., and W.D. Heyman. 2020. Considerations for offshore wind
energy development effects on fish and fisheries in the United States:
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Prairie, J.C., K.R. Sutherland, K.J. Nickols, and A.M. Kaltenberg. 2012.
Biophysical interactions in the plankton: A cross-scale review. Limnology
and Oceanography: Fluids and Environments 2(1):121–145, https://doi.org/
10.1215/21573689-1964713.
Quintana-Rizzo, E., S. Leiter, T.V.N. Cole, M.N. Hagbloom, A.R. Knowlton,
P. Nagelkirk, O. O’Brien, C.B. Khan, A.G. Henry, P.A. Duley, and others. 2021.
Residency, demographics, and movement patterns of North Atlantic right whales
Eubalaena glacialis in an offshore wind energy development area in southern
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C.L. Johnson, K. Stamieszkin, R. Ji, Z. Feng, and others. 2019. Rapid climate-
driven circulation changes threaten conservation of endangered North
Atlantic right whales. Oceanography 32(2):162–169, https://doi.org/10.5670/
oceanog.2019.201.
Sorochan, K.A., S. Plourde, M.F. Baumgartner, and C.L. Johnson. 2021. Availability,
supply, and aggregation of prey (Calanus spp.) in foraging areas of the
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AUTHOR
Grace K. Saba (saba@marine.rutgers.edu), Department of Marine and Coastal
Sciences and Center for Ocean Observing Leadership, Rutgers University,
New Brunswick, NJ, USA.
ARTICLE CITATION
Saba, G.K. 2025. Zooplankton and offshore wind: Drifters in a sea of uncertainty.
Oceanography 38(2):7–9, https://doi.org/10.5670/oceanog.2025.302.
COPYRIGHT & USAGE
This is an open access article made available under the terms of the Creative
Commons Attribution 4.0 International License (https://creativecommons.org/
licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and repro
duction in any medium or format as long as users cite the materials appropriately,
provide a link to the Creative Commons license, and indicate the changes that
were made to the original content.
Oceanography | Vol. 38, No. 2
10
SCIENTIFIC RESEARCH AND
MARINE PROTECTED AREA MONITORING
USING A DEEP-SEA OBSERVATORY
THE ENDEAVOUR HYDROTHERMAL VENTS
By Steven F. Mihály, Fabio C. De Leo, Ella Minicola, Lanfranco Muzi, Martin Heesemann, Kate Moran, and Jesse Hutchinson
FEATURE ARTICLE
The cabled TEMPO-Mini ecological observatory module at
Main Endeavour Field. Image credit: Ocean Networks Canada
and Canadian Scientific Submersible Facility – Remotely
Operated Platform for Ocean Sciences (CSSF–ROPOS)
Oceanography | Vol. 38, No. 2
10
June 2025 | Oceanography
11
INTRODUCTION
Marine protected areas (MPAs) are designated regions set aside
to manage conservation efforts, with the primary aim of pre
serving and protecting marine life. Effective conservation con
siders the overall ecosystem functions, encompassing the physi
cal, geological, and geochemical aspects of the habitat, and their
relationships with biological communities, as well as the func
tional relationship among the ecosystems within the MPA and
the neighboring undesignated marine areas (e.g., Hays et al.,
2020). Preservation efforts also extend to the cultural signifi
cance of the marine area and the sustainable use of its resources
(Gomez et al., 2021).
Managing an MPA involves balancing multiple—often com
peting—concerns, such as habitat protection and sustainable
use. Effective management must be informed by a strong sci
entific understanding of an evolving ecosystem, which requires
continuous collection of key observations. For MPAs situated
in the deep sea, this can be facilitated remotely through sensors
delivering time-series observations and recurrent collection of
physical samples that help to interpret the continuous sensor
data. However, the impacts on the protected area from sensor
deployment and data collection as well as of recurring scientific
and maintenance expeditions also need to be considered in the
MPA management plan (e.g., Cuvelier et al., 2022).
In 1984, the human-occupied vehicle Alvin confirmed the
existence of “unusually large” sulfide structures and biological
communities supported by hydrothermal venting off the west
coast of Canada (Tivey and Delaney, 1986). These structures and
communities were localized to the Endeavour Segment of the
Juan de Fuca Ridge within Canada’s exclusive economic zone.
Upon discovery, and with its fortuitous proximity to coastal
ports, the Endeavour Segment became a mecca for scientific
research, enabling the dissemination of what some describe as
its magical nature and broad recognition in Canadian society of
Endeavour’s unique features and their environmental and socio
economic significance (Tunnicliffe and Thomson, 1999).
Although the size of hydrothermal vent fields is relatively small
globally, their ecological significance is high; and even though
they are generally located in the remote deep sea, they are threat
ened by human disturbance (Van Dover, 2012). The process of
hydrothermal venting concentrates minerals at the discharge
sites, making them ideal candidates for deep-sea mining. The
scientific interest they generate can also raise threats of overzeal
ous sampling and other disturbances (Turner et al., 2019).
As a signatory to the Convention on Biological Diversity
(1993), Canada resolved to protect 30% of its oceans by 2030.
In 2003, Canada began this process by establishing the 97 km2
Endeavour Hydrothermal Vents (EHV) MPA as Canada’s first
MPA and the world’s first protected hydrothermal vent site
(Figure 1). Established under Canada’s Oceans Act, the primary
conservation objectives were to ensure that human activities in
the area contributed “to the conservation, protection, and under
standing of the natural diversity, productivity, and dynamism of
ABSTRACT. Designating marine protected areas (MPAs) is an increasingly utilized policy instrument for preserving marine eco
systems and biological diversity while also allowing for sustainable use. However, designation is only the first step and cannot
be successful without monitoring mechanisms to drive an effective and adaptive management plan. This article discusses the use
of the NEPTUNE real-time seafloor observatory—originally designed to understand the complex interdisciplinary nature of the
Endeavour mid-ocean ridge spreading center—as a tool to inform MPA management. We describe the ways in which geophysical
and geological forces control biological habitat and water column biogeochemistry, and highlight research enabled by the observa
tory that increased our understanding of Endeavour’s hydrothermal vent ecology and these dynamic processes. Endeavour is natu
rally undergoing change, so an understanding of the multidisciplinary mechanisms and factors controlling its environment provides
key management information.
FIGURE 1. The boundaries (white-lined box) and the five main active vent
clusters (shaded boxes) of the Endeavour Marine Protected Area are
delineated here on a bathymetric map. Coordinate system: WGS 1984
UTM Zone 9N. Image credit: Ocean Networks Canada
Oceanography | Vol. 38, No. 2
12
the ecosystem” and that these activities were “managed appro
priately such that impacts remained less significant than natural
perturbations” (Fisheries and Oceans Canada, 2010).
The EHV MPA is on the Endeavour Segment of the Juan de
Fuca Ridge, a section of the global mid-ocean ridge (MOR) sys
tem located in the Northeast Pacific Ocean off the west coast
of British Columbia. The MOR extends for 70,000 km through
out the global ocean and is where tectonic plates diverge and
new oceanic crust is formed. This spreading process results
in a permeable seafloor, allowing cold seawater to percolate
downward where it is heated by rising magma from the upper
mantle. During its subseafloor circulation, the seawater reacts
chemically with the surrounding crust and is eventually ejected
back into the ocean as mineral-laden, oxygen-depleted, and
superheated fluid. The process of mixing with cold, oxygen
ated seawater leads to a succession of rapid chemical reactions,
which form precipitates and creates the chimney-like hydrother
mal vents that are the hallmark of the Segment (Figure 2). As the
buoyant vent plume rises, the hot metal- and sulfide-rich hydro
thermal vent fluid continually reacts with the seawater to cre
ate dark, smoke-like, emissions highly enriched in Fe, S, Cu, Ca,
and Zn (Feely et al., 1987). The plume rises 200–300 m above the
seafloor, at which point it reaches a neutrally buoyant state and
spreads with the local oceanic currents as the chemical processes
continue (Coogan et al., 2017). This flux of vent fluids plays a
major role in maintaining the ocean’s chemical balance. Nearer
to the seafloor, chemosynthesis-based biological communities
utilize both the energy exchange occurring when these chemical
species mix with the oxygenated seawater and the chemical spe
cies themselves to form the basis of the hydrothermal vent eco
systems on the seafloor and in the water column (Van Dover,
2000; Burd and Thomson, 2015).
This paper provides an overview of the main geological, bio
geochemical, and physical processes at the Endeavour Segment
and their roles in regulating the biological communities and
habitat structures that host ecosystems at the vents and near the
seafloor. We describe highlights of the past 16 years of scien
tific research and monitoring enabled by the NEPTUNE sea
floor cabled observatory that support management decisions for
the MPA. Recently, the EHV MPA’s boundaries were repealed
and subsumed into the 133,017 km² Tang.ɢ̱ wan – ḥačxʷiqak –
Tsig̱ is (TḥT) MPA. This significantly expanded area is of cul
tural and economic significance to coastal Indigenous peoples
of the west coast of North America and is cooperatively man
aged by the Council of the Haida Nation, the Nuu-chah-nulth
Tribal Council, the Pacheedaht First Nation, and the Quatsino
First Nation, together with Fisheries and Oceans Canada
(Government of Canada, 2024).
THE NEPTUNE OBSERVATORY
In addition to its designation as an MPA, the Endeavour Segment
was also selected as one of the three Integrated Studies Sites for
the US National Science Foundation-funded Ridge 2000 pro
gram (Fornari et al., 2012) that attracted significant global sci
entific attention. Highlighting Endeavour’s scientific value, the
proposal for a NEPTUNE cabled observatory was successfully
funded, with the primary purposes to understand the spread
ing, subduction, and faulting of the Juan de Fuca plate, as well as
the ecosystems and oceanography off the west coast of Canada.
For the purposes of MPA management, the deep-sea observa
tory enhances observation and monitoring in the area.
FIGURE 2. This close-up view shows a black smoker chimney at the Main
Endeavour Field. Image credit: ONC and CSSF–ROPOS
June 2025 | Oceanography
13
Operated by Ocean Networks Canada (ONC), the NEPTUNE
observatory comprises an 840 km fiber-optic cable extend
ing from Vancouver Island across the North American and
Juan de Fuca tectonic plates to connect five major node sites
to power and the internet (Barnes et al., 2007). The western
most Endeavour node supports the scientific sensors in the
heavily instrumented Endeavour Hydrothermal Vents MPA
(Table 1, Figures 3 and 4). Real-time data, archived data, and
data products from sensors in the axial valley and on the flanks
of the Endeavour Segment of the Juan de Fuca Ridge have been
available since 2010 through ONC’s digital infrastructure,
Oceans 3.0 (Owens et al., 2022). Regular expeditions using ships
and remotely operated vehicles (ROVs) to maintain infrastruc
ture also collect observations and physical samples to ground
truth and complement the sensor data. Internet connectivity
from the ships allows the Canadian and international science
community to participate from shore to conduct experiments
and sampling strategies to aid in developing a more complete
understanding of the physical, geological, and biological pro
cesses of this protected environment (Table 1).
TABLE 1. Summary of major disciplines, sensor technology, and geological, physical, chemical, and biological properties monitored and their scientific
and MPA monitoring impacts. MEF = Main Endeavour Field. RCM = Regional Circulation Mooring North and South.
MONITORING
EQUIPMENT
PROPERTIES
MEASURED
VENT FIELD/
SITES
(See Figure 3)
SIGNIFICANCE
(Value in MPA management)
KEY PUBLICATIONS
DISCIPLINE: GEOPHYSICS AND GEOCHEMISTRY
1. Seismometers and
accelerometers
Seismic ground
motions and
low-frequency
hydroacoustic signals
• RCM-N
• MEF
• Mothra
• Ridge Flank
• Node
Identify periods of seismic unrest driven by
tectonic spreading events that are linked
to changes in venting and/or eruptions.
Also, detect chimney collapses and activity
from baleen whales.
• Krauss et al., 2023
• Bohnenstiehl et al., 2004
• Smith and Barclay, 2023
2. Bottom pressure
recorders (BPR)
Vertical seafloor
movements and sea
level changes
• RCM-N
• MEF
• Ridge Flank
• RCM-S
• Node
• Mothra
Inflation/deflation can indicate changes
in the underlying magma chamber that
affects the hydrothermal system and can
precede spreading events.
• Barreyre and Sohn, 2016
3. Benthic and
Resistivity Sensors
(BARS), paired with
vent fluid samples
Temperature,
resistivity, and redox
potential
• MEF
• Mothra
Changes in chemical composition of
vent fluids over time, and the influence
of chemical and heat fluxes on the
composition and diversity of benthic vent
biological communities.
• Xu et al., 2017a
4. Vent imaging sonar
3D vent plume and
heat flux mapping
• MEF
Hydrothermal heat and chemical flux
variability is a fundamental control on the
ecosystem.
• Bemis et al., 2015
• Xu et al., 2014, 2017b
5. Serial gas tight
sampler
Fluid geochemistry
• MEF
Changes in chemical composition of vent
fluids over time, and the influence of
chemical and heat fluxes on the makeup
and diversity of benthic vent biological
communities.
• Seyfried et al., 2022
• Evans et al., 2023
6. Water samplers
(RAS-PPS)
Water geochemistry
and biology
• MEF
Diffuse venting and its effects on the
benthic ecosystem.
• Lelièvre et al., 2017
7. Sediment traps
Particulates from
vent plumes
• MEF
• West Flank
• South Axial
Hydrothermal venting and its effects on
the water column.
• Coogan et al., 2017
• Mills et al., 2024
• Beaupre-Olsen et al., 2025
DISCIPLINE: PHYSICAL OCEANOGRAPHY
1. Regional Circulation
Moorings
Ocean circulation
and water properties
(temperature, salinity,
and density)
• RCM-N
• NW Mooring
• RCM-S
• SW Mooring
Proxy measurement of the overall heat flux
variability to the ocean from hydrothermal
venting. Current circulation in and above
the axial valley controlling larval and vent
plume chemistry dispersal.
• Thomson et al., 2003
• Xu et al. 2014, 2017b
2. Conductivity,
temperature, and
depth (CTD)
Temperature, salinity
and density, dissolved
oxygen
• Node
Near seafloor water properties.
Continued on next page…
Oceanography | Vol. 38, No. 2
14
GEOLOGY AND SEAFLOOR HABITAT
The Endeavour MPA hosts hydrothermal vent ecosystems
whose formation and persistence are directly linked to the
dynamic geological and tectonic processes of the Juan de
Fuca Ridge. Understanding this interplay through continu
ous, multidisciplinary monitoring is foundational to effective
MPA management.
The Endeavour Segment is an intermediate-rate spreading
center (full rate: ~52 mm yr–1) (DeMets et al., 2010; Krauss et al.,
2023) characterized by a 10 km long and 1 km wide axial val
ley flanked by rift crests rising 100–150 m above the valley floor.
Extensive and vigorous hydrothermal venting occurs within the
axial valley focused at five main active vent clusters spaced about
2–3 km apart (Figure 1; Kelley et al., 2012). The Main Endeavour
(MEF) and Mothra fields have received significant scientific
attention and are currently being monitored by sensors con
nected to the NEPTUNE observatory. The High Rise and Salty
Dawg fields (see Figure 1) are designated for minimally intru
sive studies and outreach opportunities (Fisheries and Oceans
Canada, 2010) and have no cabled sensors.
The uniqueness of hydrothermal venting regions, with respect
to other deep-sea benthic habitats, stems from the chemical flux
and exchange of heat between the ocean and the seafloor and
the geologically rapid change of the seafloor morphology due
to local tectonic dynamics. This leads to a chemically and phys
ically extreme environment that hosts the specialized life that
has physiologically and biologically adapted to the geologically
controlled environment. Although vent ecosystems are rare and
their global extent is small, their contribution to the understand
ing of life and their ecosystem functions and services are sig
nificant and are considered ideal candidates for designation as
Vulnerable Marine Ecosystems and recommended for Area-
Based Management Tools (e.g., Menini and Van Dover, 2019).
The Endeavour Segment features a combination of active and
inactive chimneys, edifices, and mounds along its axial valley.
The active structures cluster into the five major vent fields with
more than 400 inactive structures as well as the diffuse venting
sites interspersed among them. Conceptually, they are geolog
ically connected, and the entire ridge segment can be consid
ered a single temporally and spatially varying vent field driven
MONITORING
EQUIPMENT
PROPERTIES
MEASURED
VENT FIELD/
SITES
(See Figure 3)
SIGNIFICANCE
(Value in MPA management)
KEY PUBLICATIONS
DISCIPLINE: BIOLOGY
1. Video cameras
Video, paired with
other sensors
(i.e., temperature)
• MEF
• Mothra
Track biological community structure and
responses to venting physico-chemistry
dynamics.
• Cuvelier et al., 2014, 2017
• Lelièvre et al., 2017
• Carter, 2025
• Robert et al., 2012
• Lee et al., 2015
2. Biological samples
Whole specimens,
tissue, assemblages
and e-DNA
• High Rise
• MEF
• Mothra
Characterization of vent and vent-
periphery communities (from microbes to
megafauna).
• Perez and Juniper, 2016, 2017
• Perez et al., 2023
• Lelièvre et al., 2018
• Georgieva et al., 2020
3. Colonization
experiments
Community
recolonization/
ecological succession
• MEF
Investigate faunal colonization (from
microbes to macrobenthos) simulating
recovery from natural perturbations
(e.g., eruptions).
• Ongoing studies
4. Passive larval
trap collectors
Benthic invertebrate
larvae
• MEF
Larval ecology and genetic connectivity
among different vent, vent periphery,
and background deep-sea benthic
communities.
• Ongoing study
5. ROV video
surveys, including
photogrammetry
Habitat and benthic
community dynamics
• MEF
• Mothra
• High Rise
Track, at larger spatial scales, temporal
changes of vent community composition
and responses to natural perturbations.
• Neufeld et al., 2022
DISCIPLINE: SOUNDSCAPES
1. Cabled hydrophone
arrays
Intensity and direction
of broadband sound
• MEF
Vent activity monitoring, earthquake
detection (near and distal), marine-mammal
detection and monitoring.
• Smith and Barclay, 2023
2. Deep acoustic
lander (autonomous,
Dalhousie University)
Sound velocity,
pressure, conductivity,
temperature, salinity;
intensity and direction
of broadband sound
• MEF
Water-column properties affecting sound
propagation, vent activity monitoring.
• Smith and Barclay, 2023
TABLE 1. Continued…
June 2025 | Oceanography
15
by heat from a continuous axial magma chamber (Jamieson and
Gartman, 2020). Over at least the last 2,000 years, there have
been no large-scale eruptions with significant lava flows that
could bury these vent fields (Jamieson et al., 2013; Clague et al.,
2014, 2020). Krauss et al. (2023) attribute this to the degassing
of the axial magma chamber, which limits extrusive magmatism
and results in the mature chimneys, edifices, and mounds, both
active and inactive, that define the Segment. Concurrently, the
underlying shallow magma chamber ensures sufficient heat and
chemical flux to sustain regular hydrothermal circulation and
consistent sulfide structure growth.
Long, continuous time series of physical parameters provide
opportunities to reveal complex dynamics and ongoing evolu
tion of the vent system. For example, Barreyre and Sohn (2016)
correlated vent fluid temperatures with bottom pressure fluc
tuations and estimated the permeability of the shallow upflow
zones near hydrothermal venting using poroelasticity theory.
The study revealed that the Main Endeavour Field (MEF) pos
sesses geospatially distinct shallow upflow zones characterized
by different effective permeabilities, which sets it apart from
Lucky Strike and the East Pacific Rise, sites with different geo
logical characteristics and spreading rates.
At Smoke and Mirrors, located near the southern Benthic and
Resistivity Sensors (BARS; shown in the MEF inset in Figure 3),
Barreyre and Sohn (2016) modeled higher effective permea
bilities characteristic of a slow spreading center, such as Lucky
Strike, with lower heat flux and a thicker extrusive layer that has
ample permeable pathways. Just 150 m apart at Grotto (located
near the northern BARS shown in the MEF inset in Figure 3),
they modeled higher effective permeabilities that are character
istic of a fast spreading center, such as the East Pacific Rise, with
higher heat flux and a thinner extrusive layer more frequently
paved by volcanic activity.
Rather than attributing these differences to spreading rate, the
effective permeability likely varies due to output from the irreg
ular distribution of the underlying magma body. This is corrob
orated by anecdotal visual evidence from repeated visits show
ing the southern part of the MEF waning in black smoker output
(e.g., Smoke and Mirrors edifice), while the northern part of
the field (Grotto edifice) is growing and gaining in vigor. These
results and visual observations also imply that the magma sup
ply within intermediate spreading centers can vary in space and
time (possibly rapidly) and therefore regionally modify the ben
thic environment to host biological communities that are more
suited to fast or slow spreading centers.
Continuous geophysical monitoring, primarily using cabled
seismometers and bottom pressure recorders (BPRs, Table 1),
tracks the tectonic activity that can drive these changes in the
FIGURE 3. ONC infrastructure within the area of the Endeavour vent fields and adjacent ridge flanks. The node (orange square) powers the instru
ment platforms (white circles) that host scientific sensors connected to the internet via fiber-optic cables (white lines). Moorings—both autonomous and
cabled—are shown as yellow circles. Image credit: ONC
Oceanography | Vol. 38, No. 2
16
environment. The real-time data streams permit continuous
monitoring of seismic events and seafloor deformation, pro
viding insights into processes influencing environmental sta
bility and enabling timely responses to significant events. Since
2018, heightened seismicity has been observed by Krauss et al.
(2023), mirroring precursors to past diking events (1999–2005).
This culminated in a notable increase in activity in March 2024,
including an M4.1 earthquake and periods with up to 200 events
per hour, suggesting the segment may be approaching the next
diking event, prompting the scientific community to meet in
November 2024 to prepare for a rapid response to a major per
turbation of the system.
Understanding the chemical environment driving these eco
systems is critical. Due to the harsh environment of hydrother
mal venting regions, geochemical sensors for measuring the
continuous temporal variability of the chemistry of fluid emis
sions are very limited, and scientific research has relied predom
inantly on laboratory analysis of discrete samples obtained on
scientific expeditions. To obtain a continuous time series at high
temperature vents, ONC employed a cable-connected BARS
to measure temperature, resistivity, and redox potential (eH)
of the vent fluids in situ (Table 1). With discrete samples taken
at the beginning of the deployment and at the time of recov
ery, the continuous time series of the sensors’ measurements are
used to infer changes in fluid chemistry. However, these sensors
reside in black smoker vents with 300°–350°C fluid emission
and often do not last a full year between maintenance expedi
tions. Another method to improve time resolution of the vari
ability of chemical fluxes is to remotely collect discrete sam
ples. Currently, a serial gas tight sampler is deployed alongside a
BARS. Its containers can be remotely triggered to collect a time
series of 12 vent fluid samples (Seyfried et al., 2022). The timing
of the sampling is adapted to changes in seismicity or vent fluid
temperatures, allowing correlation between specific geological
events and vent fluid chemistry.
The current period of heightened seismicity marks a critical
phase for the evolution of the Endeavour Segment. It presents a
rare opportunity to observe a potential dike intrusion or spread
ing event that would offer valuable data for refining models of
mid-ocean ridge processes. Studying the Endeavour Segment,
with its intermediate spreading rate characteristics, provides a
key comparison point between fast- and slow-spreading sys
tems across the globe and other intermediate spreading cen
ters (e.g., the Galápagos Spreading Center). An impending tec
tonic event may cause significant shifts in hydrothermal output
(heat and chemistry), providing a natural experiment to study
the resilience and adaptive responses of the specialized vent
communities within the MPA. To better capture such an event,
Dalhousie University and the University of Washington, in part
nership with ONC, enhanced observatory capabilities by deploy
ing five autonomous ocean bottom seismometers in summer
2024; an additional 20 ocean bottom seismometers (including
replacements for the 2024 units) are scheduled for deployment in
summer 2025. This denser network will improve detection and
location of seismicity, providing crucial data for understanding
geological and tectonic processes and their impacts on hydro
thermal vent ecosystems. It will inform future MPA management
strategies regarding natural and anthropogenic disturbances.
OCEANIC ENVIRONMENT
Changes in and redistribution of heat and chemical fluxes from
the vent fields along Endeavour’s axial valley alter seafloor char
acteristics, affecting benthic ecosystems as well as the overlying
water column and the pelagic ecosystem it hosts. Not only is
the seawater chemistry directly altered, but changes in the heat
flux from hydrothermal venting affects the local ocean circula
tion through changes in buoyancy input from the rising hydro
thermal plumes. On an axial valley scale, the rising plume gen
erates inflow near the seafloor toward the hydrothermal vents,
which facilitates the retention of vent field larvae and plankton.
Conversely, the rising plume can also entrain planktonic organ
isms, moving them up into the water column where along-axis
currents can relocate them to vent sites with more retentive cir
culation, or higher up in the water column where they can be
swept away by ambient ocean currents to less hospitable ocean
environments (Thomson et al., 2003). If the organisms have the
ability to swim vertically or alter their buoyancy, they can use
this circulation to move to a preferred location. There is obser
vational evidence of larvae exhibiting this type of behavior at
other vents sites (Mullineaux et al., 2013). On the segment scale,
the off-axis propagation of the plume alters the chemistry of the
ocean (Coogan et al., 2017; Beaupre-Olsen et al., 2025) and has
a marked impact on the overlying pelagic ecosystem, enhancing
secondary productivity (Burd and Thomson, 2015).
Estimating the flux of hydrothermal fluid and heat along the
Endeavour Segment has generally been conducted by observing
water property anomalies, either by dense shipborne or autono
mous underwater vehicle (AUV) sampling. These observations
are inverted to estimate flux using the known temperature of the
vent fluid as it leaves the seafloor (Kellogg, 2011), resulting in an
overall value of heat flux over the time window of the repeated
surveys. With yearly AUV surveys (2004, 2005, 2006), Kellogg
and McDuff (2010) identified a transient anomaly over the Salty
Dawg vent field, suggesting that there is spatial and temporal vari
ability in hydrothermal flux; however, their temporal resolution
made it difficult to determine both the subseafloor causes and the
water column effects. As an alternative to annual AUV surveys
with their inherent coarse time resolution, four moorings of cur
rent meters and water property sensors (CTDs) were installed in
the axial valley of the Endeavour Segment. The array is designed
to utilize the “sea breeze effect” caused by the rising buoyant
plume. This effect relates horizontal currents to the intensity of
heat flux from the hydrothermal venting (Thomson et al., 2003);
therefore, variability in hydrothermal heat flux is continuously
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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Oceanography | Vol. 38, No. 2
18
corrosive fluids is used to monitor, in real time, the soundscape
at the site for extended periods of time. For example, PAM was
applied successfully to the detection and classification of explo
sive events at volcanically active sites (Chadwick et al., 2008).
Different features of the sounds produced by venting are
related to the physical mechanisms producing the sounds.
These, in turn, are influenced by physical parameters such as
flow rate, chimney height, sound speed, and cavity size (Little
et al., 1990; Crone et al., 2006; Smith and Barclay, 2023). Studies
aimed at establishing the connection between these parameters
and the sounds produced can, in principle, enable the contin
uous, remote, long-term monitoring and investigation of flow
rates, growth, and other aspects of the vents via PAM.
To explore the potential of PAM, ONC deployed a hydro
phone at MEF in 2018, and then upgraded the installation to a
four-element array in 2023. Additionally, Dalhousie University’s
Deep Acoustic Lander (Figure 4) was deployed and recovered
in 2021 and 2023, further augmenting the time series (Smith
and Barclay, 2023). Though still in its infancy, this study has
already detected a large number of transient (i.e., of duration
measurable in seconds or less), often impulsive, sounds char
acterizing the soundscape at MEF. These include chimney col
lapses, waterborne signals associated with earthquakes, and a
number of other sounds whose origins are being investigated.
A recent study reports that numerous such signals were cap
tured by ONC’s hydrophones during the major seismic event of
March 5–6, 2024. Through the investigation of power spectral
density, ambient-noise coherence, and cross-correlation with
other sensors at MEF, the same study highlighted other, longer-
term changes in the MEF soundscape that may be associated
with changes to the venting activity resulting from the increased
seismicity in the region (Smith and Barclay, 2024).
Finally, PAM is also being explored as a tool for environmen
tal impact assessment. Some marine organisms may use acoustic
cues to select settlement locations around hydrothermal vents
(Eggleston et al., 2016). Industrial activities, such as shipping
and deep-sea mining, can potentially interfere with the local eco
system by introducing changes in the soundscape, even though
they may be located at significant distances (Chen et al., 2021).
Understanding of the local soundscape relevant to the biological
activity of a site is an important component of an effective envi
ronmental impact mitigation strategy (Lin et al., 2019).
VENT BIOLOGY
Numerous biological studies utilizing video imagery and sam
ples collected from ROVs and submersibles have been con
ducted at Endeavour. They focused on describing the benthic
assemblages inhabiting a range of hydrothermal vent condi
tions, from those on high-temperature black smoker chimneys
to those sustained by broadly spread diffusive flows (Sarrazin
et al., 1997; Tunnicliffe et al., 1997; Lelièvre et al., 2018; Murdock
et al., 2021). The early studies of hydrothermal vent systems
described a specialized fauna characterized by low species diver
sity, high biomass, and high levels of endemicity (i.e., species
only occurring at vent environments; Tunnicliffe and Fowler,
1996; reviewed in Van Dover, 2000).
A key characteristic of typical vent fauna is successful asso
ciations between chemoautotrophic, symbiotic microorganisms
and their macroinvertebrate hosts (Lonsdale, 1977; Corliss et al.,
1979). Utilizing the chemical energy from sulfur, hydrogen,
iron, and methane, vent microorganisms fix carbon not only in
symbiont associations with host species but also as free-living
cells or in extensive bacterial mats (Dick, 2019). Host-symbiont
associations often achieve high densities and biomass surround
ing the areas of hydrothermal fluid flow. At the Endeavour
vents, the most conspicuous and abundant vent fauna assem
blages are comprised of the siboglinid polychaete tubeworm
Ridgeia piscesae, alvinelid polychaetes Paralvinella sulfincola
(sulfide worm) and Paralvinella palmiiformis (palm worm), the
limpet Lepetodrilus fucensis, and many other species of snails
(Figure 5a-d, Sarrazin et al., 1997). Studies to date have inven
toried close to 60 vent-associated species at Endeavour, with
12 endemic species not occurring anywhere else in the world
(Fisheries and Oceans Canada, 2010). Sampling of macrofauna
associated with tubeworm bushes near the Grotto edifice alone
revealed up to 31 species occurring in substrate patches of less
than 0.1 m2, and it highlighted the importance of keystone
species such as R. piscesae in creating habitat complexity that
enhances local biodiversity (Lelièvre et al., 2018).
The roles of microbial diversity and production in con
trolling large-scale nutrient elemental cycling and ecosystem
function have also been topics of studies based on the frequent
sampling at Endeavour. Samples of diffusive sulfidic vent fluids
helped to quantify microbial production pathways (denitrifica
tion, anammox, and dissimilatory nitrate reduction to ammo
nium), aiding global estimates of nitrogen (N) removal rates
to the subsurface biosphere that represent 2.5%–3.5% of total
marine N loss (Bourbonnais et al., 2012). Microbes were also
the focus of a number of studies examining vent fauna host-
symbiont relationships and population structure. The tubeworm
Ridgeia piscesae, a keystone species, was found to have the same
phylotype Gammaproteobacteria symbiont (Ca. Endorifitia
persephone) as six other tubeworm species in the Eastern Pacific,
revealing high levels of interconnectivity between the Northeast
Pacific and the East Pacific Rise vents (Perez and Juniper, 2016).
However, the same authors later uncovered multiple genotypes
within E. persephone making up the symbiont assemblages
of R. piscesae and argued that this genetic diversity could be
an important predictor of resilience to environmental change
(Perez and Juniper, 2017).
Since the installation of seafloor cables and platforms in the
axial valley of the Endeavour Segment in 2010, in situ instru
ments and sensors, including time-lapse video imagery, have
been providing new insights into the environmental controls
June 2025 | Oceanography
19
FIGURE 5. A sample of habitat heterogeneity and biological diversity of vent-associated and vent periphery fauna at Endeavour. (a,b) Black smoker
chimneys colonized by dense assemblages of R. piscesae tubeworms. (c,d) Typical assemblages that occur near diffusive hydrothermal flow, includ
ing alvinelid polychaetes (Paralvinella sulfincola, Paralvinella palmiiformis), polynoid scale worms (Branchinotogluma tunnicliffae), limpets (Lepetodrilus
fucensis), and snails (Buccinum thermophilum). (e) Field of view of the Mothra vent field observatory camera showing the seafloor partially covered
by white bacterial mats, Ridgeia piscesae tubeworms, Buccinum thermophilum gastropods, and the deep-sea spider crab, Macroregonia macrochira.
(f) Vent periphery sulfide and (g,h) basalt structured seafloor that provide habitat for corals, sponges, and mobile macro- and megafauna. Image credits:
ONC and CSSF–ROPOS
over vent species community composition and biorhythms. At
Main Endeavour Field, a video camera platform (TEMPO-Mini;
Auffret et al., 2009), installed in collaboration with the French
national institute for ocean science and technology (IFREMER),
provided nearly 10 years of continuous data. The length of the
video time series enabled analyses that, for the first time, estab
lished astronomical (tidal) and atmospheric (storm passages)
forcing as a control on vent macrofauna behavior (Cuvelier et al.,
2014, 2017; Lelièvre et al., 2017). The data revealed that mobile
macrofauna, such as sea spiders (pycnogonids) and polychaete
scale worms (polynoids), responded to the passage of win
ter storms 2.2 km above by regulating their biorhythms to the
storm-triggered cyclical oscillations in the diffusive vent flow
dynamics (Lelièvre et al., 2017). Video observations of picno
gonids and scale worms living in association with R. piscesae
tubeworm bushes that are supported by low-temperature dif
fuse venting also indicated that the animals respond to the cur
rents generated by these storms. At the latitude of Endeavour,
storm-induced currents have a four-day cycle due to the pas
sage of the storms and a 16-hour cycle resulting from the iner
tial oscillations generated by the storm winds that can propa
gate to the seafloor as inertial internal waves. As the currents
cyclically increase, they dilute the warm, low-oxygen vent fluids,
and the animals can be observed moving deeper into the bush,
disappearing from camera view. A study performed in waters
1,688 m deep at the EMSO-Azores Mid-Atlantic Ridge obser
vatory (EMSO = European Multidisciplinary Seafloor and water
column Observatory) corroborates these findings, as biologi
cal rhythms and circadian clock gene expression of the hydro
thermal vent mussel Bathymodiolus azoricus were found to be