Watermass transformation in Skagerrak

Subject: Oceanography

Level: Master project
Supervisor: Per Pemberton (SMHI)
Co-supervisor: Sam Fredriksson
 
This is a proposal for a master project. If a student has his/her own project idea that relates to our group´s research topics on Baltic Sea or Arctic Ocean modelling, we are happy to consider that as well.

Project background

The Skagerrak constitutes a link between the Baltic Sea and the North Sea and is a hotspot of complex watermass transformation processes. The major inflows are the Baltic Outflow (water that exits through the Danish Straits), the Jutland Current, and the Atlantic water (which flows in at depth). In addition, several major rivers discharge their freshwater directly into the Skagerrak. The major outflow is the Norwegian Coastal Current that leaves the Skagerrak in north-west.

The different currents connect in a highly dynamic system that sets up a mostly cyclonic circulation. Freshwater, heat and momentum exchange at the surface as well as interaction with the complex bathymetry leads to an eddy-rich region. The eddies stir the water down to smaller scales where small-scale mixing can occur, changing the properties of the water.

The complex mixing processes lead to what we call watermass transformations (WMT) where the inflowing waters are transformed into to new outflowing watermasses. These watermasses can most conveniently be characterized by their temperature and salinity signature, and a theoretical framework has been developed to study WMT in salinity and temperature space.

Using such a framework can hopefully lead to new insights of the complex transformations inside the Skagerrak region.

Project description

The aim of this project is for the student to learn WMT theory (Walin, 1977, 1982; Hieronymus et al 2014, Pemberton et al, 2015, Groeskamp et al 2019) and then apply this to the Skagerrak region.

The student will collect observations (from e.g. SMHI, VOTO …) and model data (from SMHI) and then analyze the data using WMT theory in S-T space.

Some examples of scientific questions that the student can tackle are:

• What are the inflowing and outflowing currents in the Skagerrak and what is the S-T signature and their strength, as function of time and space?
• What are the major drivers for the variability and trends of the transports of these currents?
• What are the major processes that drive the WMT inside the Skagerrak?
• Can we infer ecosystem change from transformations in S-T space?

Skills

• Python programming
• Comfortable with UNIX/LINUX-based systems
• Some knowledge of numerical methods used in oceanography

References

Walin, G. (1977). A theoretical framework for the description of estuaries. Tellus, 29, 128–136. https://doi.org/10.1111/j.2153-3490.1977.tb00716.x
 
Walin, G. (1982). On the relation between sea-surface heat flow and thermal circulation in the ocean. Tellus, 34, 187–195. https://doi.org/10.1111/j.2153-3490.1982.tb01806.x
 
Hieronymus, M., Nilsson, J., & Nycander, J. (2014). Water Mass Transformation in Salinity–Temperature Space. Journal of Physical Oceanography, 44, 2547–2568. https://doi.org/10.1175/JPO-D-13-0257.1
 
Pemberton, P., Nilsson, J., Hieronymus, M., & Meier, H. E. M. (2015). Arctic Ocean Water Mass Transformation in S–T Coordinates. Journal of Physical Oceanography, 45, 1025–1050. https://doi.org/10.1175/JPO-D-14-0197.1
 
Groeskamp, S., S. M. Griffies, D. Iudicone, R. Marsh, A. J. G. Nurser, and J. D. Zika, 2019: The Water Mass Transformation Framework for Ocean Physics and Biogeochemistry. Annu. Rev. Mar. Sci., 11, 271–305, https://doi.org/10.1146/annurev-marine-010318-095421.

Contact

Per Pemberton
Email: per.pemberton@smhi.se