Abstract. The Coastal Observing System for Northern and Arctic Seas (COSYNA) was established in order to better understand the complex interdisciplinary processes of northern seas and the arctic coasts in a changing environment. Particular focus is given to the German Bight in the North Sea as a prime example for a heavily used coastal area, and Svalbard as an example of an arctic coast that is under strong pressure due to global change. The automated observing and modelling system COSYNA is designed to monitor real time conditions, provide short-term forecasts and data products, and to assess the impact of anthropogenically induced change. Observations are carried out combining satellite and radar remote sensing with various in situ platforms. Novel sensors, instruments, and algorithms are developed to further improve the understanding of the interdisciplinary interactions between physics, biogeochemistry, and the ecology of coastal seas. New modelling and data assimilation techniques are used to integrate observations and models in a quasi-operational system providing descriptions and forecasts of key hydrographic variables. Data and data products are publically available free of charge and in real time. They are used by multiple interest groups in science, agencies, politics, industry, and the public.

Abstract. The Coastal Observing System for Northern and Arctic Seas (COSYNA) was established in order to better understand the complex interdisciplinary processes of northern seas and the Arctic coasts in a changing environment. Particular focus is given to the German Bight in the North Sea as a prime example of a heavily used coastal area, and Svalbard as an example of an Arctic coast that is under strong pressure due to global change.The COSYNA automated observing and modelling system is designed to monitor real-time conditions and provide short-term forecasts, data, and data products to help assess the impact of anthropogenically induced change. Observations are carried out by combining satellite and radar remote sensing with various in situ platforms. Novel sensors, instruments, and algorithms are developed to further improve the understanding of the interdisciplinary interactions between physics, biogeochemistry, and the ecology of coastal seas. New modelling and data assimilation techniques are used to integrate observations and models in a quasi-operational system providing descriptions and forecasts of key hydrographic variables.

Determination of spectral absorption coefficients in seawater is of interest for biologic oceanographers for various reasons, but faces also several problems, especially if continuous measurements are required. We introduce the flow-through-point source integrating cavity absorption meter (ft-PSICAM) as a new tool for the continuous measurement of spectral absorption coefficients in a range of 400-710 nm. A description of the system is given and its performance in comparison with a conventional PSICAM has been evaluated on two cruises in 2011 in the southern part of the North Sea (German Bight). Furthermore, factors influencing the measurement are discussed. When comparing the data of both systems, a good linear correlation has been found for all wavelengths (r² > 0.91). Deviations between systems were different with respect to the wavelength examined with slopes of linear fits between 1.1 and 1.65 and offsets between-0.1 and 0.01, with the higher values at shorter wavelengths. They were caused mainly due to contamination of the flow-through system during operation by phytoplankton particles. Focus was also laid on the measurement of chlorophyll-a concentrations ([chl-a]) and total suspended matter concentrations ([TSM]) on the basis of absorption coefficient determination. For this, appropriate relationships were established and [chl-a]-and [TSM]-values were calculated from the relevant ft-PSICAM absorption coefficients. Their progression matches well with the progression of fluorescence and turbidity measurements made in parallel. In conclusion, the ft-PSICAM is successful in measuring spectral absorption coefficients continuously and resolving relative changes in seawater optical properties.

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To meet the requirements of increasing environmental awareness in aquatic ecosystems, optical techniques offer a fast and reliable opportunity for a wide range of applications providing high-resolution measurements. In this respect, important parameters which have to be addressed include phytoplankton biomass and taxonomic composition, total suspended matter, dissolved organic matter, as well as hazardous substances, e.g., polycyclic aromatic hydrocarbons (PAHs). Requiring comparable low effort, optical methods are a convenient and noninvasive way to derive information on the optical active substances in different water bodies. Various approaches and devices are available, either aiming on the determination of the water's inherent optical properties or on measuring the fluorescence properties of different constituents. This contribution presents the objectives and measurement principles of two new optical sensor developments in this respect. A special focus lies on an integrating cavity approach for hyperspectral absorption measurement. This approach overcomes two common problems in classical absorption measurement of seawater: 1) usually low concentration of absorbing material in the water negatively affecting accurate measurements of untreated samples; and 2) errors introduced by light scattering of particles requiring empirical corrections to obtain good accuracy. To combine these advantages with the possibilities of automated, long-term high-frequency measurements, an integrating cavity was adapted for flow-through operation. First field results obtained by the resulting Hyperspectral Absorption Sensor (HyAbS) in the North Sea and off the Norwegian coast are evaluated and compared with discrete measurements. The second development is a matrix-fluorescence sensor with flexible wavelength configuration for the detection and characterization of dissolved substances, such as fluorescent dissolved organic matter (FDOM) and PAHs. Here, the measurement principle of the sensor and first field results from a related, laboratory-based method will be presented as a preliminary work necessary for the development of the final in situ sensor. Furthermore, future plans for both instruments as well as a possible combination will be discussed. In summary, both approaches have the potential to be multiparameter instruments for high-resolution measurements of environmental parameters.Index Terms-Fluorescent dissolved organic matter (FDOM), hyperspectral absorption, in situ measurements, matrix fluorescence, ocean observatories, sensor development.

Investigation of phytoplankton biodiversity, ecology, and biogeography is crucial for understanding marine ecosystems. Research is often carried out on the basis of microscopic observations, but due to the limitations of this approach regarding detection and identification of picophytoplankton (0.2-2 μm) and nanophytoplankton (2-20 μm), these investigations are mainly focused on the microphytoplankton (20-200 μm). In the last decades, various methods based on optical and molecular biological approaches have evolved which enable a more rapid and convenient analysis of phytoplankton samples and a more detailed assessment of small phytoplankton. In this study, a selection of these methods (in situ fluorescence, flow cytometry, genetic fingerprinting, and DNA microarray) was placed in complement to light microscopy and HPLC-based pigment analysis to investigate both biomass distribution and community structure of phytoplankton. As far as possible, the size classes were analyzed separately. Investigations were carried out on six cruises in the German Bight in 2010 and 2011 to analyze both spatial and seasonal variability. Microphytoplankton was identified as the major contributor to biomass in all seasons, followed by the nanophytoplankton. Generally, biomass distribution was patchy, but the overall contribution of small phytoplankton was higher in offshore areas and also in areas exhibiting higher turbidity. Regarding temporal development of the community, differences between the small phytoplankton community and the microphytoplankton were found. The latter exhibited a seasonal pattern regarding number of taxa present, alphaand beta-diversity, and community structure, while for the nano-and especially the picophytoplankton, a general shift in the community between both years was observable without seasonality. Although the reason for this shift remains unclear, the results imply a different response of large and small phytoplankton to environmental influences.

The concentration of chlorophyll-a ([chl-a]) and total suspended matter ([TSM]) are important parameters in biological oceanography. [Chl-a] is a commonly used proxy for estimating phytoplankton biomass while [TSM] also includes detrital material and mineral particles and thus influences light attenuation and photosynthetic activity in the water column. For characterizing the distribution (patchiness) of both parameters adequately over a longer time period, fast and effective measurement methods are required that can also be applied in situ or continuously. Thus, alternatively to direct determination of [chl-a] and [TSM], optical proxy values are often measured. The PSICAM is an integrating cavity approach for measuring absorption coefficients of water constituents with high precision which can be used also continuously (flow-through-PSICAM). In this study, the performance of these absorption measurements for [chl-a] and [TSM] determination was evaluated and compared with the performance of traditional approaches using chl-a fluorescence and turbidity measurements. Data were collected in the German Bight (North Sea) in 2010 and 2011. For [chl-a], fluorescence measurements are compared with pigment absorption coefficient values at a 2 wavelength of 676 nm (a Φ 676 nm), while the [TSM]-proxies were turbidity and particle absorption at 700 nm (a p 700 nm). As reference data, HPLC-determined [chl-a] and gravimetrically determined [TSM] were used. Our results showed linear relationships between [chl-a] and fluorescence or a Φ 676 nm , respectively. Coefficients of determination (R²) were in a range of 0.71 to 0.88, with the higher values related to the absorption measurements. Furthermore, it was demonstrated that fluorescence underestimates [chl-a] depending on ambient photosynthetically active radiation (PAR). Linear relationships were also observed between [TSM] and its optical proxies with R² values between 0.93 and 0.98. Turbidity measurements appeared to be influenced to a certain extent by the physical properties of the suspended material, resulting in a slightly higher variability than the a p 700 nm measurements. Absorption measurements turned out to be promising optical proxies for determining [TSM] and [chl-a] due to their lower variability compared with the other proxies. This improved accuracy could be already partially achieved also for continuous measurements. Moreover, a combination of the different optical methods has the potential to provide additional information besides concentration, such as the source of TSM in the water or physiological condition of the phytoplankton.