Characterising the seasonal response of the mixed-layer and the transitional-layer to the passage of storms in the sub-Antarctic Zone

Abstract

Mid-latitude storms occur over large distances in Southern Ocean (SO. and have been shown to drive substantial vertical mixing leaving behind enormous wakes of perturbed upper ocean. The vertical extent and duration of the impact of these storms on the upper ocean remains unknown in this region, partly due to lack of observations in this remote part of the world. The mixed-layer depth (MLD. is used widely as proxy for vertical extent of upper-ocean mixing with the assumption that it reflects the integrated variability of atmospheric forcing. However, the responses of the vertical extent of the MLD and the transitional layer depth (TLD. where sub-MLD mixing may occur has been shown to vary substantially between storm events at similar locations. In this study, these two-physical metrics, the MLD and TLD, have been used to better characterise the response of the upper ocean mixing to storms in the Sub-Antarctic Zone (SAZ. and to further interrogate the relevance of the MLD as a proxy for mixing extent at these temporal scales. This is explored under different seasonal conditions using data collected from high-resolution autonomous robotic platforms (gliders., which remotely sampled the SAZ from spring to summer documenting the passage of several strong storm events. Two types of gliders are used in pseudo-mooring mode: a deep-profiling Sea-glider collecting the density structure from the surface ocean to 1000 m and circling this glider is a Wave-glider, which is at the surface measuring wind intensities and changes in atmospheric pressure. The findings of this work are important because storms on MLD regulate iron to the upper ocean vertical structure, and iron contributes towards phytoplankton growth required for the ocean productivity. We are also hoping to see how reliable MLD is as a metric for turbulence in the SO. - Abstract as displayed in the - Abstract booklet. The presentation on the day may differ from the - Abstract.