Dive FD-214 · Northwest Indian Ocean · 2026-02-19
Carlsberg Ridge
A hydrothermal field on a slow-spreading ridge, mapped at metre resolution for the first time.
- Max depth
- 3,480 m
- Bottom temp
- 2.1 °C
- Vessel
- RV Sounding
- Lead
- Dr Anjali Varma
Notes
The Carlsberg Ridge spreads at roughly twenty-two millimetres a year, which is slow enough that the vent structures survive long enough to build. What we expected was a scatter of small chimneys. What the multibeam returned was a field of them, the tallest standing eleven metres, in an area the size of a football pitch.
Water chemistry at the vent mouths came back at 341 degrees, hot enough that the sampling arm sheath had to be swapped between the second and third approach. Around them, at three metres, the water is at ambient: two degrees. That gradient across a body length is the entire reason this ecology is strange.
The survey ran eleven hours on the bottom across two days. Everything below is from the descent log and the onboard sensor package, published unedited.
Logged on the bottom
- —Vent chimneys, 34 counted, tallest 11.2 m
- —Scaly-foot gastropods on three chimney bases
- —Shrimp aggregation, estimated 4,000 individuals
- —Bacterial mat, continuous, roughly 90 m across
Descent
Sunlight, 0 to 200 m, is the band at the top too thin to letter.
Water column, descent cast
| Depth | Temp | O₂ | Note |
|---|---|---|---|
| 0 m | 28.4 | 6.6 | Surface, monsoon-warmed |
| 200 m | 17.1 | 4.2 | Base of the sunlight zone |
| 800 m | 8.3 | 0.4 | Oxygen minimum layer |
| 1,500 m | 4.1 | 2.1 | Oxygen recovering below the minimum |
| 2,800 m | 2.4 | 3.4 | Deep water, near-uniform |
| 3,480 m | 2.1 | 3.3 | Seafloor, vent field margin |
Oxygen in millilitres per litre. Casts are raw, uncorrected for sensor drift.