# When the Ocean Keeps a Logbook: A CTD Profile in Six Steps | Ocean Archive

URL: https://oceanarchive.net/stories/ctd-profil-i-sex-steg

Temperature, salinity, oxygen — a CTD is like a receipt for how the water column 'feels', layer by layer.

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Data story

Temperature, salinity, oxygen — a CTD is like a receipt for how the water column 'feels', layer by layer.

![Ocean Archive Editorial](https://oceanarchive.net/placeholder.svg)

Ocean Archive Editorial

January 8, 2026

4–6 min read

Some stories can't be photographed. They have to be measured. A CTD profile is one of the clearest ways to see how the ocean is built in layers — and how those layers change over time.

### WHAT IS A CTD?

CTD stands for Conductivity, Temperature, and Depth. The instrument records how water properties change with depth, producing a "profile" of the water column.

### WHY CONDUCTIVITY?

Because conductivity helps estimate salinity. And salinity, together with temperature, affects density — which influences how water masses form layers and move.

### SIX STEPS — FROM DECK TO DATASET

- Plan the station (where, when, why here?)

- Lower the instrument through the water column

- Record a continuous profile

- Quality control (spikes, drift, plausibility)

- Document (metadata: instrument, calibration, units)

- Publish the dataset (for research, education, visualisation)

##### What we know / What we don't (yet)

- What we know: what the sensors measured at a specific time and location.

- What we don't always know: why a shift happens without more measurements, models, and context.

### MAKE DATA HUMAN (WITHOUT BREAKING PRECISION)

A good data story answers:

- What am I looking at?

- Why does it matter?

- What do we need to measure more of?

- What can I do with this (learn, contribute, share)?

RELATED MEDIA

#### IN THE ARCHIVE

Archive search: coming soon

DATASET

OA-0010

##### CTD_profile_station_X.csv

Nordic Waters

Archive

Raw CTD profile data with temperature, salinity, and depth measurements.

© Ocean Archive

Open Data

PHOTO

OA-0011

##### Temperature vs depth

Data Visualization

Graphic showing temperature variation across the water column.

CC BY

OA-0012

##### Deployment on deck

Research Vessel

CTD rosette being prepared for deployment from the research vessel.

CC BY-NC