Dive FD-198 · Central Indian Ocean · 2025-06-27
Ninety East Ridge
A seamount summit survey, and an octopus nursery nobody expected at this latitude.
- Max depth
- 2,110 m
- Bottom temp
- 2.7 °C
- Vessel
- RV Sounding
- Lead
- Dr Rehan Qureshi
Notes
Ninety East is the straightest thing on the ocean floor, a ridge running north to south for five thousand kilometres with barely a bend in it. This dive took the summit of one seamount along it, at 2,110 metres.
The survey was routine until the third transect, which crossed a rock overhang holding roughly two hundred brooding octopuses, each sitting on a clutch. Nurseries like this are known from the eastern Pacific and were not expected here.
We logged it, photographed it, took no samples, and left. Some findings are better as a coordinate somebody else can revisit.
Logged on the bottom
- —Brooding octopuses, ~200, on one overhang
- —Cold seep indicators, shimmering water
- —Coral, three morphotypes, unidentified
- —No sampling taken at the nursery site
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 | 27.8 | 6.7 | Surface |
| 150 m | 21.4 | 5.1 | Mixed layer base |
| 900 m | 6.9 | 1.1 | Low oxygen |
| 2,110 m | 2.7 | 3.1 | Seamount summit |
Oxygen in millilitres per litre. Casts are raw, uncorrected for sensor drift.