Johan’s sampling mission began the day after leaving Cape Town harbour. He samples the surface ocean for a number of biogeochemical properties at high resolution across the fronts. These fronts separate very distinctive water masses in the Southern Ocean; each of these waters masses as well as each of the fronts have a “fingerprint” combination of properties, such as temperature, salinity, oxygen and nutrient contents. For example, as you can imagine, the sub-tropical waters are warmer that the sub-antarctic waters further south. These two water masses are separated by the Subtropical Front, roughly at ~40°S, whereas another front further south, the Subantarctic Front, roughly located between ~44 and 45°S, separates the sub-antarctic water from the polar water. South of the Subantarctic Front, we find the Antarctic Circumpolar Current (ACC), forming a belt around Antarctica. This is the most important current in the Southern Ocean and you might have heard of this area as the Roaring Forties, since the prevailing westerly winds driving the ACC are extremely strong. A third front even further south, the Polar Front, roughly located at ~50-51°S, separates the polar water from the Antarctic water. These fronts can be around 80 km in width! They usually show enhanced primary productivity, due, for instance, to the upwelling of nutrients from deeper, nutrient-rich waters. Consequently, they also provide suitable foraging conditions and are often visited by marine predators.