By Liz Comer
There was once a blob of water milling around in the ocean minding its own business until a bunch of scientists came along in a research vessel (us on Discovery) and sampled it. To sample water, scientists lower instruments and bottles over the side on a rosette frame (as shown in the picture below). The instruments contain sensors to measure pressure, temperature, salinity, oxygen, the available light for algae to live in the ocean and the murkiness and colour of the water. The water flows through these sensors (red arrow in picture) or is trapped in the bottles (yellow arrow in picture). Last year a fish even managed to get stuck in one of the sensors which offset the measurements. These two forms of sampling are then analysed separately; the sensor measurements are processed on a computer and bottle samples in lab based instruments. The images below show these lab instruments; imagine the confusion in setting up the nutrient analyser! The salinity is analysed in a separate room, nicknamed the salt mine, due to the need for a stable temperature for the instruments to work reliably.
The two separate measurement streams, bottles and sensors, are then compared. The result of this process is a calibration where the sensor measurements are corrected using the bottle sample measurements. With this step complete, the blob of ocean water has been observed and its properties are ready to be recorded in a database back on dry land.