No, this is not about any of us going swimming in the 3°C seawater! It’s instead about calibrating the Microcat sensors that were placed on our moorings. These instruments were put on the moorings to measure temperature, pressure and conductivity (from which we derive salinity) over a year. In order to check that these values are accurate, we strap the instruments (seen on the picture below) to the CTD frame for a so-called “calibration-dip”. The CTD is then stopped for 6 minutes at a number of different depth levels, during which we obtain measurements of temperature, pressure and conductivity from both the Microcats (which have a relatively slow response time) and from the carefully calibrated CTD itself. This ensures that we are able to detect any drifts or offsets in the Microcat data.