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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 08/07/2026

The news is out today in @nature.com ! The OHA-GEODAMS observatory had the incredible luck to capture a major seafloor spreading event back in 2024, just 2 months after its deployment. You can read all about it at: www.nature.com/articles/s41... Here’s how it unfolded 👇

nature.com

Anatomy of a seafloor spreading event captured by in situ seismogeodesy - Nature

By combining hydroacoustic, direct-path ranging and bottom-pressure measurements, in situ observations of a rifting event at a segment of the Southeast Indian Ridge are reported, providing insight int...

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 09/02/2026

What a day! We visited Kerguelen station, met king penguins and elephant seals, and walked on the "Desolation Island". Just a few days before reaching the OHA-GEODAMS area, this was an unforgettable stop in the middle of the Southern Ocean. Cheers to the penguins 🐧

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 03/02/2026

On our way to the Southeast Indian Ridge and it’s all hands on deck 🚢🔧 From building tripods for acoustic beacons to installing the transducer and modem in the ship’s forward hold, operational prep is well underway!

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 24/01/2026

The 2026 GEODAMS team safely arrived close to Possession Island in the Crozet archipelago a few days ago. A penguin crowd welcomed us under a very bright sky and with the traditional croziflette that follows... 🐧 🍽️ We’ve had our fill, both for the eyes and the stomach.

Penguin crowd at la Manchotière from Possession Island

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 20/01/2026

The OHA-GEODAMS team is back to document how the Indian Ocean grows. Cruise #3 on board Marion Dufresne left La Réunion Island a few days ago to maintain the multi-sensor observatory on the South East Indian Ridge. Follow us on this new adventure! (credit photo: Ewen & Didier)

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 01/02/2025

Last, but not least, we also recovered and re-deployed an A-0-A pressure sensor, right in the middle of the ridge's axial valley. This state-of-the-art instrument corrects its own drift by regularly re-calibrating itself against an inner chamber where the pressure is known.

An A-0-A pressure sensor, encased in a frame attached to four buoys floating on the ocean surface, waiting to be picked up. Credit: J.-A. Olive, LG-ENS / FOF

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 31/01/2025

The core of the OHA-GEODAMS project is to measure active deformation for 3 years on the Southeast Indian Ridge and the Amsterdam transform fault. To this end, in February 2024, we deployed 15 acoustic beacons that have been pinging each other every few hours ever since.

2 iXblue/Exail Canopus acoustic transponders encased in yellow floats, atop 2-m tall metal tripods, waiting to be deployed on the back deck of R/V Marion Dufresne during the 2024 GEODAMS cruise. Credit: J.-A. Olive, LG-ENS / FOF

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 30/01/2025

We also recovered and redeployed five hydrophones that were first deployed last year during the #GEODAMS 2024 cruise.

a hydrophone encased in an orange float just surfaced right in front of the R/V Marion Dufresne, on a calm sea. Credit: J.-A. Olive, LG-ENS / FOF

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 30/01/2025

For the last ~10 days, we've been hard at work on and around the Southeast Indian Ridge at 37ºS to recover and redeploy a bunch of geophysical instruments. Let's break it down 👇

Regional map of the Southeast Indian Ridge near Amsterdam Island

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 20/01/2025

A few days ago, we deployed a Sea Explorer glider developed by ALSEAMAR and owned by ENSTA Bretagne at the location of our first hydrophone, southeast of Amsterdam island.

Julie & Jean-Arthur bringing the glider to the workboat for deployment. Credit: E. Klein

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 19/01/2025

As we make our way to our study area, we map the seafloor under the ship! 🌊 Our multibeam echosounder sends acoustic waves to the ocean floor and records how much time they take to bounce back.

Data coming live from the ship's multibeam echosounder

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 19/01/2025

Planning our upcoming deployments like they schedule sketches on Saturday Night Live (with multiple new versions since that v1 😜) #GEODAMS

@sismolise.bsky.social and @jaodynamics.bsky.social trying to figure out the most efficient schedule of operations in front of a post-it-covered whiteboard

a whiteboard covered in colored post-it notes representing the order of our instrument recoveries and deployments

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 15/01/2025

It was too windy for us to set foot on Kerguelen today, so instead we did laps in the Gulf of Morbihan, waiting for conditions to improve. We were eventually able to pick up ~20 scientists leaving the research station at sunset, and got to enjoy some stunning views!

map showing the ship going around in circles (or rather rectangles) in the Gulf of Morbihan waiting for the wind to die down. Credit: A. Briais. FOF.

the shores of Kerguelen. Credit: J.-A. Olive

picking up new passengers in Kerguelen. Credit: J.-A. Olive

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 14/01/2025

A tradition aboard the Marion Dufresne is to stamp letters to be mailed from the French Southern and Antarctic Lands. The ship captain, chief mechanic, doctor... each have their own stamp, and the science teams make new, custom ones every year!

@jbeesau.bsky.social carefully applying an official Marion Dufresne stamp on the mail. Credit: C. Dimier

the official OHA-GEODAMS 2025 stamp: an illustration of our seismo-geodetic network across the mid-ocean ridge + the glider listening to whale sounds. Credit: J.-Y. Royer

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 13/01/2025

We're back in business after a rough storm west of Kerguelen! We're now sheltered from the waves (but not the wind!) in the Gulf of Morbihan, enjoying our first views of the island and prepping the logistics of next week's deployments.

big wave crashing against the prow of R/V Marion Dufresne. Credit: S. Furst

barometer highlighting the low-pressure zone (965 hPa) we just went through. Credit: S. Furst

Kerguelen island in the distance. Credit: J.-A. Olive

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Reposted by The OHA-GEODAMS Seafloor Observatory

Lise Retailleau @sismolise.bsky.social · 10/01/2025

Yesterday @geodams.bsky.social

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 05/01/2025

For several days now, several species of seabirds have been making their way with us. We've seen: the great albatross, the sooty albatross, yellow-billed albatross, black-browed albatross, giant petrels, white-chinned petrels and many others whose identification is not always easy.

black-browed albatross. Credit: Julie Béesau

white-chinned petrel. Credit: Julie Béesau

yellow-billed albatross. Credit: Julie Béesau

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 02/01/2025

Today we were treated to spectacular views of Crozet's Possession Island and East Island, while the local penguins put on quite a show! 🐧🌤️⛰️

the cliffs of Crozet's Possession Island. Credit: S. Furst

the spectacular cliffs of Crozet's East Island in the distance. Credit: S. Furst

curious penguins swimming all around the ship. Credit: S. Furst

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 01/01/2025

Happy new year from the R\V Marion Dufresne! Our journey began last year on xmas day, by heading straight South from La Réunion to the Crozet Islands.

$The R\V Marion Dufresne making its way through some fog$

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 31/12/2024

Our target site is located on the Southeast Indian Ridge, near Amsterdam Island. But to get there, the R/V Marion Dufresne will first loop across the Southern Indian Ocean to do all kinds of oceanographic and geochemical measurements, and swing by the Crozet Islands and Kerguelen. #OBSAustral2025

Our planned route across the Southern Indian Ocean. Credit: Claire Lo Monaco

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 31/12/2024

The goal of #GEODAMS is to deploy and maintain the first-of-its-kind seafloor seismo-geodetic observatory across a mid-ocean ridge and adjacent transform fault, to document seafloor spreading as it happens on a time scale of a few years.

Schematic overview of the OHA-GEODAMS observatory. Credit: J.-A. Olive & J.-Y Royer

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The OHA-GEODAMS Seafloor Observatory @geodams.bsky.social · 26/12/2024

Hi! We are the OHA-GEODAMS team, a research project documenting how the Indian Ocean grows in (almost) real time. Between 2024 and 2027, we'll have 4 cruises to maintain a seafloor seismo-geodetic observatory across the Southeast Indian Ridge. We just started cruise #2, follow our adventures here!

a cloudy sunset from the R/V Marion Dufresne

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