Tracing the Warming and Salinification Processes in the Conveyor Belt; from the Drake Passage to the Tropics

Water mass transformation is an important driving mechanism for the oceanic circulation, and plays a crucial role for the northward flowing water masses in the Southern Ocean. Here, the northward Ekman transport drives cold and fresh water masses towards the Pacific, Atlantic and Indian oceans. As the water is transported away from the Southern Ocean, it increases in temperature and salinity, either by air-sea interactions or internal mixing. These northward flowing water masses are part of the thermohaline Conveyor Belt, connecting the ocean basins.

In the present study, Lagrangian trajectories are used to trace the water mass transformation of the northward flowing water masses in the Southern Ocean; from the Drake Passage until reaching 20°C. The results show that these water masses reflect a warming and salinification in this part of the Conveyor Belt circulation.

Further, to describe the mechanism of warming and salinification, trajectories are classified depending on their paths and end positions. Two classes are found: (1) trajectories ending in a latitudinal band around the globe just south of Australia and, (2) trajectories ending further into the different ocean basins mainly near the equator. The primarily results show that the first class is mainly warming near the surface due to air-sea interactions. In the second class trajectories are divided into sub classes, where the main contributor is the water that directly enters the Pacific Ocean. This water is subducted, and caught in the equatorial undercurrent where it reaches the surface and 20°C in the eastern parts, leaving internal mixing as the root cause to the warming and salinification.

These results show how changes in temperature and salinity drives the Conveyor Belt and its path from where the North Atlantic Deept Water upwells in the Southern Ocean, until it reaches 20°C further north.