Salting the sea

Ulf Riebesell by Ulf Riebesell on 20.10.2018

Why would anyone salt the sea? Isn’t it salty enough? Well, that may be the case, but that’s not the point here. The point is that the two parameters we can measure most precisely in the sea are temperature and salinity. Well not actually salinity, but conductivity, which we can use to calculate salinity when we know the temperature. In oceanography measurements of salinity/conductivity and temperature are widely used to characterize different water masses and follow their flow around the globe. We also measure them in our mesocosms to see whether the enclosed water is well mixed or stratified and to determine the amount of rainfall into and evaporation out of our enclosures.

However, we can also use salinity measurements to calculate the mesocosm volumes. And this is how it goes: We add a small amount of salt to our mesocosms. Well, small in relative terms, compared to how much is already in the seawater. In absolute terms it’s actually a lot more than you would use for cooking in your entire life. We measure the salinity in our mesocosms before and after the addition. From the amount we have added, which we weigh very precisely, and the observed increase in salinity, we can then calculate the exact volume of the enclosed water. And that’s the whole purpose of this exercise.

The salt-addition team did a great job preparing the brine solution, filling it in numerous 20 L bottles, shipping them out to our mesocosms and adding the salty soup into the enclosures. It was a sad moment, however, when they returned back after completing their mission. The instrument measuring salinity and temperature – along with 5 other environmental parameters – broke down.

The rest of the evening was spent trying to spot the problem. Unfortunately without success. Damn it! That’s even worse than a broken coffee machine – the multi-sensor is so critical for our research. It allows us to sense the “heartbeat” of our mesocosms. No time to loose, let’s get it to the manufacturer as fast as we can. Sidney will take the first flight tomorrow morning to get our multi-sensor baby to the manufacturer back in Germany. Let’s hope they can fix it.

Salt-addition team on their way to salt the sea Salt-addition team on their way to salt the sea – with lots of bottles filled with brine solution.