In the North Atlantic Ocean, warm and salty surface waters are transported northward and are responsible for a relatively mild climate in Europe. In the deep sea, cold and fresh waters flow southward. This circulation is also known as overturning. Due to climate change, this overturning is predicted to weaken, potentially impacting the European climate. For better predictions of those future changes, long-term ocean observations are needed to monitor the currents contributing to this overturning process.
The aim of this thesis was to better understand the mechanisms driving one of those currents in the Irminger Sea, southeast of Greenland: the Irminger Current (IC). The IC brings warm and salty waters from the subtropics northward. With the use of instruments that record current velocity, temperature, and salinity, I showed that the strength of the IC on long-time scales is driven by changes in the ocean’s density over the entire Irminger Sea. I further showed that in response to very low salinity waters that arrived in the IC in 2016, the current brings lighter waters northward with a potential impact on overturning. I also studied where the waters feeding the IC come from. One part originates from further east, in the Iceland Basin, but some waters also originate from the Irminger Sea itself.
As the IC contributes to the overturning, mechanisms, and changes described in this thesis are important to better understand potential future changes in overturning.
