Chart showing the diverse measuring platforms of the submesoscale expeditions exploring ccordinated a submesoscale eddy. -image: HZG-
The global ocean circulation is driven by wind, solar radiation, tides, and the exchange of heat and fresh water with the atmosphere. While the global importance of this large-scale structured flow has been known for a long time, high-resolution model simulations have only recently revealed that the ocean and coastal areas are dominated by variability on multiple spatial and temporal scales. In this context, processes in the submesoscale range (10 m to 10 km, lifetime of hours to days) have gained a great deal of attention recently. One reason for this shift in attention is the significant improvement in observational technology and model resolution now emerging as capable of detecting such small-scale structures.
The Clockwork Ocean Expedition -SubEx2016-
Zeppelin NT during Expedition Clockwork Ocean over the Baltic Sea -image: HZG-
In order to better understand the physical submesoscale dynamics and their close interaction with biogeochemical processes and phytoplankton, the division Operational Systems developed a unique multi-platform capability for very-high resolution observations.
The Expedition Clockwork Ocean, which took place in the Southern Baltic Sea in June 2016, was therefore a great success and showed for the first time the development of a submesoscale eddy from generation to decay – in unprecedented resolution.
Submesoscale features have very short life spans on the order of 6 – 12 h and often measure only a few hundreds of meters in diameter. Measurements were therefore carried out for up to ten hours per day so that submesoscale features could be detected and repeatedly observed before their decay.
A motorglider plane was equipped with an infrared camera to find submesoscale processes by detecting their strong surface temperature gradients.
Furthermore, a 75-meter-long zeppelin was outfitted with a cooled infrared camera and a hyperspectral push-broom sensor to observe the dynamics and physical-biological coupling of the features. It was the first time, that a zeppelin was used in coastal or marine sciences. It served as a coordination and communication center during the expedition, enabling the near-real time exchange of data crucial for these targeted high-resolution measurements.
The real-time data transmission of temperature maps from the zeppelin to several vessels was crucial for measuring fronts and eddies in situ and following them during their quick temporal evolution. HZG’s research vessel Ludwig Prandtl, the research vessel Elisabeth Mann Borgese, and the speedboat Eddy as well as ocean gliders, autonomous robots, and drifters were used to deliver the most detailed in situ observations.
The HZG's research vessels Ludwig Prandtl and Eddy measuring a submesoscale structure during Expedition Clockwork Ocean. -image: HZG-
The speedboat Eddy was purchased and outfitted with a winch, FerryBox, ADCP, and weather station. In addition to Ludwig Prandtl, it served as a platform for a Towed Instrument Chain (TIC) that was developed by this Research Unit for measurements at several depths simultaneously at high speeds. Currently, up to twenty CTDs (with additional chlorophyll or oxygen sensors) can be deployed, even from small vessels, and towed at speeds of up to ten knots covering the upper 45 m of the water column. The real-time data transmission of all sensors is currently under development. Ocean glider operations have been optimized for shallow water environments with heavy traffic. For small-scale observations, they are equipped with turbulence probes and an ADCP. Ship-based radar observations were used to detect surface currents, waves, and surface features, such as fronts.
The division Operational Systems has built in PACES II a worldwide unique observational multiplatform capability that led to the most detailed observations worldwide of submesoscale processes to date.
A submesoscale eddy with a diameter of approximately 200 m. The high-resolution temperature imagery showed the first observations of the evolution of a submesoscale eddy from its generation to its decay. -image: HZG-
It is now possible to resolve processes with a 1-5 m and 5-20 min resolution for areas as large as 10 x 10 km2, or an unprecedented resolution of <1 m and <1 s for areas of 0.5 x 0.5 km2.
The observations show extreme frontal gradients of typically 1°C over 5 m; vertical velocities of > 1 cm s-1; Rossby numbers of 10 – 20; and presumably off California the first observations of hydraulically controlled flow not directly influenced by topography in a two-layer flow with Froude numbers on the order of one. Further highlights are the first observations of a submesoscale eddy generation, through subsequential stationary aerial measurements.
ROMS Model of the Baltic Sea with a resolution of 100 m. High relative vorticity indicates strong submescale activity. -image: HZG-
The observations show intense mixing within some submesoscale eddies leading to short eddy life times of approximately 12 h, which is associated in some eddies with a rapid export of waters with high chlorophyll concentration to subsurface waters, indicating an important contribution to the carbon pump.
The strong coupling of physical and biogeochemical processes is confirmed by observations showing high phytoplankton concentrations in the immediate vicinity of eddies and fronts. Individual eddies have been tracked to derive first estimates of the dissipation of kinetic and potential energy over their lifetimes. Regional Ocean Modeling System (ROMS) modeling with resolutions of 100 m and a Large Eddy Simulation (LES) model are currently in use for comparison, and larger-scale interpretation of field measurements.
Further observations will be carried out as part of the Helmholtz project MOSES in 2019 off the Cape Verde Islands to observe the interaction of submesoscale and mesoscale flow as well as in 2020 to investigate the role of submesoscale eddies during deep convection events in the Mediterranean Sea’s Golfe du Lion.
Merckelbach, L. (2016): Depth-averaged instantaneous currents in a tidally dominated shelf sea from glider observations, Biogeosciences, 13, 6637-6649, doi:10.5194/bg-13-6637-2016
Huang, W.,Carrasco, R., Shen, C., Gill, E.W., Horstmann, J., Surface Current Measurements Using X-Band Marine Radar With Vertical Polarization, IEEE Transactions on Geoscience and Remote Sensing, 54, no. 5, 2988-2997, 2016. doi:10.1109/TGRS.2015.2509781
Carrasco, R., Streßer, M., and Horstmann, J.: A simple method for retrieving significant wave height from Dopplerized X-band radar, Ocean Sci., 13, 95-103, 2017a, doi:10.5194/os-13-95-2017
Carrasco, R., Horstmann, J., Seemann, J.,Significant Wave Height Measured by Coherent X-Band Radar, IEEE Transactions on Geoscience and Remote Sensing, 55, no. 9, 5355-5365, 2017b,
Lund, B., Haus, B.K., Horstmann, J., Graber, H.C., Carrasco, R., e, Near-Surface Current Mapping by Shipboard Marine X-nd Radar: A Validation, Journal of Atmospheric and Oceanic Technology, submitted 2017
The Clockwork Ocean Project: Website, Full Dome, VR
The Project Clockwork Ocean logo. -image: HZG-
For more information, visit the CLOCKWORK OCEAN WEBSITE.
The award winning cross-media Project Clockwork Ocean was developed jointly with the Public Relations Office at HZG to inform the public about a highly relevant research topic and a unique observational approach to marine sciences.
An immersive cross-media approach was used to transport the audience directly into the setting of the experiments and to trigger fascination for scientific discovery in a largely unknown environment.
Scene from the full animated full dome movie Clockwork Ocean. -image: HZG-
The project comprises the development of a mobile planetarium, two planetarium films, a virtual reality (VR) media player, the use of 360° videos, VR glasses, and a parallax webpage.
Both planetarium films are part of regular program screenings at several planetariums, such as in Hamburg, Berlin, Kiel, or Nuremberg. The film Clockwork Ocean received the special award for “Best of Science Visualisation” at the Fulldome Festival in Jena in 2016.
The Mobile Dome used as HZG's own planetarium-image: HZG-
The mobile planetarium was custom built for HZG and is intended for science communication at festivals. It measures 9.5 m in diameter with a thirty-two person capacity. Its six projectors and tilted dome allow for an exciting immersive media experience. The dome was used at several festivals, such as at the national celebrations for the Day of German Reunification in Frankfurt/Main 2015, Dresden 2016, and Mainz 2017 or the climate conference COP23 in 2017.
The Minister of Energy, Agriculture, the Environment, Nature and Digitalization of Schleswig-Holstein Dr. Robert Habeck experiencing the VR. -image: HZG-
It was also part of a meeting at the Representation of the State of Schleswig-Holstein in Berlin 2016 and contributed to the Greenscreen festival in Eckernförde in 2015. During these festivals, the film typically reaches an audience of 1,200 people per day.
The German film poster for the full dome movie Mysterious Oceans - The Eddy Hunt. -image: HZG-
The Expedition Clockwork Ocean, however, also received an unusual amount of public attention. During the zeppelin’s transfer flight from Lake Constance to Berlin, life Internet coverage by the television channel WDR directly from the zeppelin as well as a flight over downtown Berlin sparked a great deal of interest, culminating in two top ten spots of Twitter Trends in Germany that day as well as 1100 online articles.
The extensive press, radio, and television as well as blogging coverage during the experiment reached more than 150 million people in June 2016. Real-time data transmission during the experiments allowed the public to follow the experiments.