The Sea Has Layers
See how ocean temperature changes between shallow and deeper water through the year.
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How to explore
Water can have different temperatures at different depths. This project follows sensors at one coastal station in Nova Scotia to show how that difference changes through the year.
Choose a year
Start with 2024 and follow the daily difference between 10 and 30 metres.
Choose a month
See the average temperature at four depths and compare that month across years.
Compare years
See how the selected month's average temperature difference varied across six years.
- Metre
- A unit of distance; here it gives the sensor's estimated depth below the low-tide waterline.
- °C
- Degrees Celsius, a unit of temperature; a difference of 2°C means one sensor was two degrees warmer than another.
- Daily average
- The average of accepted temperature readings from one sensor depth on one date.
- Temperature difference
- The 10 metre daily average minus the 30 metre daily average; a negative value means deeper water was warmer.
Birchy Head · Nova Scotia · 2019–2024
The sea has layers.
See how ocean temperature changes between shallow and deeper water through the year.
These sensors sat at 10 to 30 metres below the low-tide waterline. The difference changes with the seasons, and can even reverse.
Start here
Choose a year
Follow the temperature difference day by day. Start with 2024, then choose another year to compare the pattern.
01 / Through the year
When is the upper sensor warmer?
Each narrow bar is one day in 2024. Bars above zero mean the water at 10 metres was warmer than at 30 metres; bars below zero mean it was cooler. Choose a month below to see its depth profile and compare it across years.
On these days, the 10 metre sensor was at least 2°C warmer than the 30 metre sensor. The 2°C mark is a simple comparison threshold, not a biological safety limit.
The shaded section marks January. Scroll the chart sideways to see later months on a small screen. The bars show daily averages from fixed depths, not temperatures throughout the whole water column.
Read the monthly differences as numbers
| Month | Difference | Days at least 2°C warmer |
|---|---|---|
| January | −0.6°C | 0 of 31 |
| February | −0.4°C | 0 of 29 |
| March | +0.1°C | 0 of 31 |
| April | +0.9°C | 1 of 30 |
| May | +2.2°C | 15 of 31 |
| June | +2.6°C | 16 of 30 |
| July | +1.8°C | 7 of 31 |
| August | +3.7°C | 31 of 31 |
| September | +4.9°C | 24 of 30 |
| October | +2.0°C | 12 of 31 |
| November | +0.6°C | 4 of 30 |
| December | −0.3°C | 0 of 31 |
02 / Down the water
A look below the surface
This profile shows the average daily temperature at four sensor depths in January 2024. Read from top to bottom: deeper sensors sit lower on the chart. Choosing a different month or year changes this shape.
Average difference between 10 and 30 metres. A minus sign means 30 metres was warmer.
- 10 metres
- 3.7°C
- 15 metres
- 3.9°C
- 20 metres
- 4.1°C
- 30 metres
- 4.4°C
Scroll the chart sideways on a small screen; the values are listed below it. Dots mark sensor depths, not a continuous reading between them. Each monthly value averages the daily averages; all days in the selected month are present.
03 / Across years
Did January look the same each year?
Each bar shows the average daily temperature difference for January, in degrees Celsius. Bars right of zero mean 10 metres was warmer; bars left mean 30 metres was warmer. Choose a year to bring it into the charts above.
For January, the monthly difference ranges from −1.1°C to −0.2°C across these six years. These records show variation at one site; they do not establish a long-term climate trend or explain what caused a particular year.
Why this exists
The question
How does the temperature difference between 10 and 30 metres at Birchy Head change by season and from year to year?
What to try
Choose a year, then choose a month to follow the temperature difference down the water column.
Method and limits
About the data
I used the March 31, 2026 TidyTuesday daily reduction of the Province of Nova Scotia's Lunenburg County Water Quality Data, collected by the Centre for Marine Applied Research at Birchy Head. Its published cleaning script excludes source readings whose temperature quality flag is Fail, then averages retained readings by date and sensor depth. I retrieved the daily file on September 20, 2026 at TidyTuesday commit f4d1b35ca09d8c0d875451635daef9179adfc9e0 and retained 2019–2024, the six complete calendar years with a value on every day at 10, 15, 20, and 30 metres. The original daily series has 19,165 rows; this static reduction covers 2,192 dates. Daily difference is the published 10 metre mean minus the 30 metre mean. For each month and depth, I average the daily means with equal weight per date. The monthly 2°C count uses the unrounded daily differences. Displayed monthly temperatures and differences round to one decimal place. Sensors record fixed estimated depths below low tide, not an entire water column, and tides alter their actual depth below the surface. This one-station record cannot isolate causes or establish a long-term climate trend.
Skills used
- Data analysis
- Data engineering
- Information design
- Interaction design
- Visual design
- Editorial storytelling
- Accessibility
- Performance
What the data shows
- At Birchy Head, the 10 metre sensor was cooler than the 30 metre sensor on average in January and February in all six complete years, but warmer on average in August in all six years.
- The 10 metre sensor was at least 2°C warmer than the 30 metre sensor on 110 days in 2024 and 161 days in 2023. A six-year difference at one station does not establish a climate trend.
- In August, the average daily difference ranged from 3.66°C in 2024 to 6.31°C in 2019 across the included years.