Master´s thesis defense by Ida Ringgaard – Niels Bohr Institute - University of Copenhagen

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Master´s thesis defense by Ida Ringgaard

Title: The impact of near-inertial waves on the Arctic halocline

In recent years the Arctic sea ice has been observed to decrease, leading to more exposed ocean surface and enhanced turbulent mixing. Near-inertial waves have been observed to enhance through interference with the wind, and to penetrate down into the cold halocline layer. It has been suggested that near-inertial waves in the Arctic Ocean could become strong enough to penetrate through the cold halocline layer and into warmer waters, potentially causing a warming of the surface mixed layer.

In this study, the impact from near-inertial waves on the Arctic halocline and mixed layer are investigated using the Hybrid Coordinate Ocean Model (HYCOM). Three different model resolutions are used: A coarse model resolution, a model with finer vertical resolution and a model with finer horizontal resolution. The model is compared to two sets of observations, one from April 2007 and one from 2008-2009, to estimate how well the model performs for specific events.

The model is found to have weaker velocities and stratification compared to both observations used for comparisons, and with previous studies. Increasing the vertical resolution increases the velocity and stratification in the four events in 2005. The opposite is seen when comparing to the two specific sets of observations. Increasing the horizontal resolution does not change the current velocity significantly, but it causes a change in the atmospheric field. The cold halocline layer is not observed in any of the three model setups. The near-inertial waves is in this study observed to penetrate into the halocline, but not through it.