Thermohaline staircases in the Caribbean Sea
J.O. Koetsier (TU Delft - Civil Engineering & Geosciences)
C. A. Katsman – Mentor (TU Delft - Environmental Fluid Mechanics)
Julie D. Pietrzak – Graduation committee member (TU Delft - Environmental Fluid Mechanics)
C. G. van der Boog – Graduation committee member (TU Delft - Environmental Fluid Mechanics)
Henk A. Dijkstra – Graduation committee member (Universiteit Utrecht)
Leo R.M. Maas – Graduation committee member (Universiteit Utrecht)
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Abstract
Thermohaline staircases are characterised by stepped vertical temperature, salinity and density profiles, which are formed and maintained by the double diffusion of heat and salt. Because double diffusion is the primary mixing agent in regions with staircases, it is the topic of extensive studies. Previous studies, however, are mainly theoretical and modelling orientated and observational evidence is needed to verify the results. In our study we use an extensive dataset with 460 vertical profiles of temperature and salinity. We found that staircases in the Caribbean Sea are related through temperature and salinity, indicating that
staircases in the Caribbean Sea are constant in time and space. Individual steps, however, differ and were characterised in four types: well-developed steps, transitional layers, inversions and absence of steps. A case study of a strong anticyclonic eddy gave the indication that steps are influenced by short term processes. The eddy induces lateral gradients and hereby positions the water masses in the interior and exterior of the eddy such that thermohaline
intrusions are initiated. The apparent preconditioning by the eddy, leading to thermohaline intrusions, allows us to speculate that the eddy is a catalyst in double diffusive diapycnal buoyancy transport.