Speaker: Julia Muchwski, PhD student at the Department of geological sciences

Vertical mixing leads to vertical fluxes of e.g. salt, heat, nutrients and other dissolved substances in the ocean, in fjords, estuaries and lakes. The distribution of salt and heat drives the thermohaline circulation of the world’s oceans and affects the residence time of the deep water. Locally, vertical mixing affects the water properties and composition with depth and is important for marine ecosystems.

The interior of marine bodies (away from the seafloor or coastlines) mixes comparatively little. Instead, a major part of the total internal mixing is caused by flow over rough bathymetry. In the Baltic Sea, 90% of the mixing is related to seafloor bathymetry. This bathymetry-related turbulent mixing is dynamic and locally confined, and therefore under-resolved by established observational in situ methods.

Our study area, the Åland Sea, is a hotspot for mixing due to its extremely rough bathymetry. On two cruises with R/V Electra in 2019 and 2020 we collected acoustic broadband data together with in situ measurements of dissipation rates of turbulent kinetic energy. We found that our acoustic observations reveal the detailed structure of turbulent mixing with radically increased resolution compared to in situ measurements alone. In this seminar, I will give some background information on vertical mixing, introduce the very special Åland Sea region and then discuss the potential and limitations of using R/V Electra’s acoustic system to map and quantify turbulent mixing. I will further show some preliminary results from a current project, in which we try to use the acoustic observations to improve estimates of vertical salt and heat fluxes across the halocline in the Åland Sea region.

IGV Seminar Series organizers
Wei-Li Hong, wei-li.hong@geo.su.se
Paola Manzotti, paola.manzotti@geo.su.se
Christian Stranne, christian.stranne@geo.su.se