The term “submesoscale” refers to physical features in the ocean whose size ranges between approximately 100 m and 10 km. Submesoscale features have recently been the subject of intense study, as it is has been suggested that these features are very important in many ocean processes (e.g., ocean energy transfer, vertical transport, primary production).
Submesoscale features are difficult to observe because:
- their location of origin is difficult to predict
- they are generally too small to be detected using traditional aerial imaging and shipboard monitoring
- they only exist for a short time (hours to a few days)
- they generally move with the prevailing currents, making them difficult to track
The detection and observation of submesoscale features therefore requires a network of innovative observational techniques connected in real-time. The network is depicted in the artistic image, and currently includes:
(1) Airborne remote sensing; infrared cameras mounted on an airplane or zeppelin are used to identify the location of a submesoscale feature (e.g., eddy or front) by detecting characteristic changes in the sea surface temperature.
(2) This location information is used to guide a high-speed boat to the feature.
(3) After arrival, the boat makes continuous passes across the feature, while towing a long string of sensors behind it. This effectively maps the eddy’s horizontal and vertical structure of temperature, bulk density, and chlorophyll a, among other variables. We are currently in the process of developing an improved combination of a towed sensor array and a high-speed boat.
(5) More vessels arrive and measure other variables, such as current speed and direction, surface roughness and surface biofilms.
(6) The airborne observations are continuously updated to guide the vessels, allowing them to continue to measure until the feature is no longer visible from the air.
The continually evolving methods have been successfully applied off the coast of California, and will soon be tested in the Baltic Sea.
We want to use the resulting data to find out if energy is generated and/or dissipated at these scales and determine the importance of the submesoscale in the local energy cascade. Furthermore, we want to know how submesoscale features may affect phytoplankton growth; for example, by increasing the transport of nutrients from deep to shallow water.
Our work is part of an international collaboration, and includes the HZG working groups Radar Hydrography and Remote Sensing.
The underwater glider is an autonomous underwater vehicle (robot) that profiles the water column in an undulating fashion along pre-programmed transects. A typical payload contains a CTD for measuring temperature and salinity profiles, turbidity sensors (estimating concentrations of suspended sediment) and fluorescence, (estimating the abundance of cholorophyll A). An important feature of gliders is the long endurance of up two months, during which about 1500 km can be covered. A satellite communication system makes glider data available in near-real time, so that the data can be used in data-assimilation procedures to improve the prediction skill of regional circulation models. The high temporal data resolution also makes gliders an ideal platform for process studies. An example of such a process is the resuspension of sediment due to currents and wave action. In contrast to ship-borne measurements, glider measurements are not restricted to weather conditions or time slots for ship time.
In the framework of COSYNA, cruises by research ships across the German Bight provide a quasi-synoptic overview of the German Bight three to four times per year. The towed undulating vehicle system Scanfish ™ MK II (EIVA) collects highly-resolved vertical and horizontal profile data of the water column to complement the regular COSYNA in-situ and remote sensing data of the ocean surface. The Scanfish ™ is equipped with CTD sensors, optical devices to study the distribution and content of phytoplankton and suspended solids. Scientific studies will comprise the understanding of the position of the chlorophyll maximum in the German Bight or the relevance of the vertical density distributions for the data assimilation in regional operational observation systemsOverview Scanfish data during Ship cruises - accessible by link from COSYNA Regular Ship Cruises
For more than ten years, the department is conducting long-term measurements in the tidal flat areas of the German Bight, utilising observation poles, bottom-mounted systems, and waverider buoys. The objective of these activities is to test new data acquisition systems and data transmission tools. The collected time series are analysed in terms of exchange processes between the tidal flat areas and the German Bight. The buoys measure only parameters related to the sea state, while the bottom-mounted systems acquire oceanographic state variables like pressure, temperature, conductivity, velocity, and turbidity. in addition on the poles are registered fluorescence, photosynthetic active radiation, pH-value, oxygen and atmospheric parameteres like air pressure, temperature, wind speed, humidity, irradiation, and precipitation.Updated Pole Data - accessible by link from COSYNA Wadden Sea Poles Observations Complete Pole Database from 1997 until today - accessible by link from COSYNA Time Series Database