Mixation II

Ocean turbulence consists of chaotic and intermittent motions that enhance ocean mixing on length-scales ranging from millimeters to hundred kilometers. Due to technological, financial and logistical limitations, ocean mixing can't be measured directly on global scales. Yet, numerical models that simulate ocean and climate dynamics require us to specify ocean mixing strengths. Hence, we develop simplification method, i.e. parameterizations, to still include this mixing. Unfortunately, the results from climate models, are very sensitive to choices in these parameterisation, meaning that they need to be further constraints by means of observations. As observations are thus impossible to obtain and the required scales, we develop theories that provide indirect estimates of mixing, from variables that we can measure on global scales or at high frequencies. This cruise aims to provide observations that can calibrate two such methods that will provide ocean mixing estimates. With these methods calibrated, we can produce estimates of global, full-depth and time varying maps of mesoscale and small-scale mixing strengths. These maps will constrain and improve parameterisations and thus ocean and climate models. With this cruise we will collect observational data with which we will: Main Goal: Calibrating the Spiraling inverse method. Main Goal: Calibrating Mesoscale mixing parameterisations. This includes estimating inermittency of mesoscale mixing and studying topographic mixing suppression. Bonus 1: Study topographic Rossby Waves and cross-slope mixing. Bonus 2: Study influence of mesoscale mixing on Nitrate fluxes (with University of Liverpool). The first goal is to calibrate the Spiraling Inverse Method (SIM). For this method, a certain amount of spiralling of temperature-gradient along neutral surfaces is required. This region has these characteristics but is also known for having significant amount of both small-scale and mesoscale mixing. Hence, the chosen location has the required ingredients to be able to calibrate the SIM. The second goal is to calibrate a new mesoscale mixing parameterization that includes effects of mean-flow suppression and topographic suppression effects. The resulting parameterization is then used to study intermittency of mesoscale mixing. The latter is rarely studied but impacts heat and tracer fluxes and needs to be included in future parameterizations for numerical ocean models. Then there are two bonus topics. One of them is study characteristics of Topographic Rossby Waves in this region and understand how they suppress mixing and transport tracers. The second one is to understand the effect of mesoscale mixing on interior to surface transport of Nitrate. An important aspect of the carbon cycle. The latter is a collaboration with Universities in the UK. In the framework of this research 4 moorings have been deployed within the EEZ of Bermuda. The current application is for recovery of these moorings