A synthesis of loss-on-ignition measurements and remote sensing data to elucidate space-time variations in the organic fraction of total suspended matter in a coastal environmen

The exchange of particulate matter between intertidal fringes and pelagic regions is of central interest for coastal biogeochemistry, as it specifies inorganic and organic matter flux. A major difficulty in integrated coastal zone management is to determine and quantify where and how nutrients and pollutants imported from land become distributed and transformed within coastal regions. Surface distributions of total suspended matter (TSM) concentrations can be derived from extensive analyses of remote sensing data. But these data provide, however, no qualitative information about the characteristics of suspended particles.

The central idea of our study is to go beyond spatial-temporal variations of bulk TSM concentrations and introduce additional information about the organic matter (OM) content of TSM. For this purpose we take advantage of a set of nearly 3000 in situ TSM and Loss-on-Ignition (LoI) sample data. We introduce a parameterization (LoI model) that distinguishes between two OM fractions incorporated in TSM. One fraction is described in association with mineral (or lithogenic) particles. The other represents a seasonally varying OM fraction of TSM. Our LoI model was calibrated against seasonally sorted LoI data from the Southern North Sea, but a comparison with coastal data from Pearl river, Scheldt estuary and Limfjord will also be presented. Based on maximum likelihood estimates of model parameters we apply our LoI parameterization to remote sensing data derived from MERIS/ENVISAT-TSM products of the German Bight.

Our model-based analysis of remote sensing data exhibits specific qualitative features of TSM within the German Bight. Most interestingly, we can resolve a transition zone between the Wadden Sea and deeper pelagic regions of the Southern North Sea where lithogenic associated OM appears in concentrations comparable to those of fresh OM. We will discuss how this transition is indicative for a zone of effective particle interaction and sedimentation. The dimension of this transition zone varies between seasons and with location. Our generic LoI model can be easily calibrated against in situ measurements and can be applied to remote sensing TSM products and any type of TSM data of other coastal regions in order to elucidate space-time variations in the OM fraction of TSM.