Surface boundary layer dynamics
We study how fronts, filaments, and eddies shape air–sea exchange by controlling stratification, mixing, and vertical transport in the ocean’s surface boundary layer (SBL). This upper layer, typically characterized by relatively weak density stratification, connects the atmosphere to the ocean interior by mediating fluxes of momentum, heat, freshwater, and gases, while strongly influencing the light–nutrient environment that regulates primary productivity.
Using the Baltic Sea as a natural laboratory, we combine high-resolution observations with nested, eddy- and submesoscale-permitting simulations based on GETM. These approaches allow us to resolve processes from spatial scales of kilometers and temporal scales of hours—where submesoscale fronts, vortices, and filaments emerge—while linking them to their larger regional impacts.
A recent focus of our work is the detection and analysis of coherent structures and their associated transport pathways. Using Lagrangian eddy-tracking methods together with long, high-resolution model simulations, we quantify where eddies form, how long they persist, how far they propagate, and how effectively they isolate or exchange water masses. These analyses reveal how coherent structures organize horizontal stirring and create localized hotspots of mixing and vertical exchange.
By combining these diagnostics with tracer and particle-tracking studies, we connect surface-boundary-layer dynamics to transport pathways relevant for biogeochemistry and ecosystems—for example through eddy-driven stirring and submesoscale processes that can influence the development and persistence of phytoplankton blooms.
This work contributes to the Collaborative Research Centre TRR 181 Energy Transfers in Atmosphere and Ocean and is closely coordinated with the Turbulence and Small-Scale Processes group to improve process understanding and parameterizations across the range from turbulence to balanced motions.
Selected publications
Cahill, B., Chrysagi, E., Vortmeyer-Kley, R., Gräwe, U., 2024. Deconstructing co-occurring marine heatwave and phytoplankton bloom events in the Arkona Sea in 2018. Front. Mar. Sci. 11. https://doi.org/10.3389/fmars.2024.1323271
Chrysagi, E., L. Umlauf, P. Holtermann, K. Klingbeil, H. Burchard (2021) High-resolution simulations of submesoscale processes in the Baltic Sea: The role of storm events. Journal of Geophysical Research (Oceans). 10.1029/2020JC016411.
Chrysagi, E., Basdurak, N.B., Umlauf, L., Gräwe, U., Burchard, H., 2022. Thermocline Salinity Minima Due To Wind‐Driven Differential Advection. JGR Oceans 127, e2022JC018904. https://doi.org/10.1029/2022JC018904
Jacobs, E., Bittig, H.C., Gräwe, U., Graves, C.A., Glockzin, M., Müller, J.D., Schneider, B., Rehder, G., 2021. Upwelling-induced trace gas dynamics in the Baltic Sea inferred from 8 years of autonomous measurements on a ship of opportunity. Biogeosciences 18, 2679–2709. https://doi.org/10.5194/bg-18-2679-2021
Vortmeyer-Kley, R., Berthold, M., Cahill, B., Gräwe, U., Feudel, U., 2025. Unraveling the Influence of Short-Lived, Three-Dimensional, Eddy-Like, Coherent, Oceanic Structures on Phytoplankton Dynamics and Nutrient Transport. Journal of Geophysical Research: Biogeosciences 130, e2025JG009107. https://doi.org/10.1029/2025JG009107
Vortmeyer-Kley, R., Holtermann, P., Feudel, U., Gräwe, U., 2019. Comparing Eulerian and Lagrangian eddy census for a tide-less, semi-enclosed basin, the Baltic Sea. Ocean Dynamics 69, 701–717. https://doi.org/10.1007/s10236-019-01269-z