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.

Data story

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

Ocean Archive Editorial

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)?

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IN THE ARCHIVE

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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