News

Improved description of the North Sea from a combination of techniques. A Deltares-IVM publication with Marieke Eleveld and Hans van der Woerd

Mud in the water column plays an important role in the ecology of shelf seas such as the southern North Sea. This so-called Suspended Particulate Matter (SPM) influences the underwater light climate, which is an important environmental factor for phytoplankton growth. The North Sea sediment transport system is characterized by highly variable concentrations in time and space: resuspension events during high wave conditions, variable river discharge and tidal currents all contribute to the complexity of the system

The new paper with Marieke Eleveld and Hans van der Woerd as co-authors presents a method to accurately describe the spatial and temporal patterns of SPM in the southern North Sea. Such descriptions can improve the understanding of the dynamics of the coastal environment, but they also serve environmental monitoring and evaluation programmes such as for the expansion of the harbour of Rotterdam (IVM Newsletter 2008).

Until the late 1990s, the description of the dynamics of SPM in the North Sea mostly relied on national monitoring programmes (ship-based sampling), occasionally complemented with dedicated scientific field campaigns. Nowadays, automated in situ monitoring buoys enable the recording of continuous time series of SPM at an increasing number of sites for prolonged periods of time. Moreover, with the arrival of reliable ocean colour remote sensing data, more frequent synoptic mapping of sea surface SPM has become feasible with increasing spatial resolution. Three-dimensional, process-based modelling can provide complementary information about the coastal transport system.      

In order to achieve a more accurate synoptic (overall) description of the coastal SPM, Deltares and IVM set up a pilot study (funded by NIVR and with participation of the Port of Rotterdam) to apply data assimilation by means of Ensemble Kalman Filtering (EnKF). Data assimilation combines model output with measurement data, using the information on the uncertainties in the model and the measurements to give an optimal estimate of the SPM concentrations in the coastal system.

The figure illustrates the effect (top) of assimilation of SPM from remote sensing (bottom right) into the model (bottom left) which originally overestimated the effect of the outflow of relatively clear Rhine River water.

The resulting paper is now available as:

El Serafy, G.Y., Eleveld M.A., Blaas, M., van Kessel, T., Gaytan Aguilar, S., van der Woerd, H.J., 2011. Improving the description of the suspended particulate matter concentrations in the southern North Sea through assimilating remotely sensed data. Ocean Science Journal 46(3): 179-204. doi: 10.1007/s12601-011-0015-x