New knowledge on ocean mixing | PhD defence Niek Kusters

Department

Themes

Wave

Niek Kusters studied mixing in the ocean. He used various methods and datasets to estimate the strength of mixing based on measurements and observations. His research helps to approximate mixing processes in the ocean more accurately: relevant for the climate, ocean circulation and the uptake of atmospheric CO2, for example. Kusters will defend his thesis on February 2nd.

Ocean mixing is one of the most critical yet poorly constrained processes in the climate system. Ocean mixing consists of many processes acting on various scales, from millimeters to over 100km and from seconds to months. This way, ocean mixing affects the uptake, transport and storage of tracers, such as heat and carbon, thereby influencing the climate, ocean circulation and other phenomena such as Oxygen Minimum Zones, hydrological cycles and sea-level rise. 

Understanding the climate

To increase our understanding of the climate and future projections thereof, a better understanding of the magnitude and drivers of these mixing processes is needed. However, both in modelling and observational studies, the mixing occurs at scales that are not fully resolved. Either because the model resolution is too coarse or the observation scales are insufficient in time and space. 

Sensitive to unconstrained choices

Therefore we rely on parameterizations: approximations based on larger scale variables. These parameterizations are sensitive to unconstrained choices but can be improved by observationally-based constraints. Observationally-based estimates of the mixing strength, obtained in this thesis, help to improve our understanding of mixing processes and to improve parameterizations of ocean mixing used in modelling studies. 

Among other things, Kusters collected and used high resolution observations of small-scale, deep ocean turbulence. He compared the observations of two types of sensors and compared these with estimates from parameterizations based on standard, lower resolution data. In particular, he focused the comparison on the case of very weak turbulence.

Autonomous underwater buoys

Currently Kusters is continuing his research at the University of Southampton, where he is working on equipping autonomous floats with turbulence sensors and obtaining autonomous measurements of deep ocean turbulence.