Black Sea · 5 July 2024
At 100 metres, only 1.2% of peak oxygen remained
The probe read 10.65 mg/L at 23 metres. At 100 metres, it read 0.125 mg/L. Both values come from the same descent.
1,001 m · 1,011 readings · one column of water
The vertical journey
Descend to the end of the profile.
Scroll or drag the control. The readings change with depth while the paper strip keeps the probe’s trace.
Seven casts reaching at least 500 metres
The line moves.
91–157 m
Oxygen fell below 0.2 mg/L in all seven casts. The threshold appeared at different depths, ranging from 91 to 157 metres.
0.2 mg/L marks water with only trace oxygen left. It is a descriptive threshold used here to compare profiles.
Same day · same depth
At a station 29 km away, the probe read 3.815 mg/L versus 0.125 mg/L.
Eight hours and 29 minutes later, at a station to the south-east, the readings at 100 metres formed a ratio of 30.6 to 1.
Now take the controls
Choose one of the nineteen casts.
The map shows every profile recorded between 5 and 9 July 2024. The chart opens on the first 200 metres, where the decisive change occurs; you can extend it to the final reading.
Depth at which O₂ falls below 0.2 mg/L
cast ended before the threshold
The oxygen axis expands 0–1 mg/L so that trace values remain visible.
Three profiles that tell the story
Why it happens
The water remains layered.
Less saline water rests above saltier water. The density difference weakens vertical mixing, so atmospheric oxygen mainly ventilates the upper layer. Below it, decomposing organic matter consumes the oxygen that reaches deeper water.
Sources and precision
About the measurements
The 19 profiles were recorded by the Middle East Technical University Institute of Marine Sciences aboard R/V Bilim-2 between 5 and 9 July 2024, in Turkish waters of the south-western Black Sea. The probe measured pressure, temperature, salinity, dissolved oxygen, pH, oxidation–reduction potential, fluorescence, turbidity and light.
Depth is calculated from pressure and latitude. Readings shown between measured levels are linearly interpolated. “Below 0.2 mg/L” means the first downward crossing of that value. Some casts stopped above the reported seabed; the page shows only the section that was actually measured.
Oxygen extremely close to zero is difficult to measure with absolute precision. The page preserves the sensor readings and uses 0.2 mg/L as a comparable threshold rather than turning small readings into an artificial zero.
The Zenodo record’s description says “September 2024”, but its title, collection dates and all nineteen profile timestamps indicate 5–9 July 2024. The page uses that consistent interval.