Report - Research Cruise on the Elisabeth Mann Borgese to the Skagerrak by Grete Boskamp

My name is Grete Boskamp and I am an associated PhD student of the TRR 181, based at the Leibniz Institute for Baltic Sea Research Warnemünde (IOW) in Rostock. My research focuses on water mass transformation and energy dissipations in submesoscale fronts. A process by which water masses of different origins mix and change their properties at relatively small spatial scales, doing that they transfer energy from larger scales to smaller scales.

This April, we set out on a research cruise aboard the Elisabeth Mann Borgese to the Skagerrak, the strait connecting the North Sea and the Baltic Sea. The Skagerrak is an exceptional natural laboratory for our purposes: it is a region where multiple water masses not only meet but are actively formed, and its relatively compact size makes it feasible to capture the most relevant features within a single campaign and to model the underlying processes at very high resolution.

We departed from Rostock and were joined by colleagues from the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Oldenburg, as well as a group from the University of Gothenburg. The cruise had two main scientific objectives. The first was a series of transects using a microstructure profiler, a free-falling instrument that measures pressure, temperature, salinity, and small-scale velocity shear as it descends through the water column. Under certain assumptions, the shear measurements can be interpreted as turbulent dissipation rates, which are a key quantity for quantifying mixing and, ultimately, water mass transformation. The second focus was the deployment and recovery of surface drifters some floating devices equipped with GPS and various sensors, which allow us to track the velocity of the uppermost water layer. In frontal regions, where water masses of different densities converge, horizontal velocities but also temperature and salinity fields can vary considerably over short distances, making the drifters a valuable tool for mapping the horizonal variations.

One of the defining experiences of this cruise was how often we had to adapt our sampling strategy to the weather. Wind and wave conditions frequently forced us to measure at locations other than originally planned. This might turnout to be a fortunate constraint: it gave us a natural opportunity to compare the oceanic state before, during, and after strong wind events – a perspective that will likely prove scientifically valuable when we analyse the role of atmospheric forcing in driving energy dissipation and water mass transformation at the front.

Ship time is precious, and to use it as efficiently as possible, we worked in shifts around the clock. The standard system is a 4-8 rotation: four hours on, eight hours off – though in practice, responsibilities often extend into the rest period. Despite the demanding schedule, research cruises have a very particular atmosphere that I always look forward to. In this small, self-contained community, everyone works closely together towards the same goal. Whenever new data came in, the excitement was shared across the whole team. These small things make fieldwork, with all its unpredictability, remains one of the most rewarding parts of this kind of research.