Monika zabłocka

Institute of Oceanology Polish Academy of Sciences · Department of Marine Physics

The main goal of the project is to determine diffusion coefficient of identified DOM fraction from pore waters into near bottom water, and to determine the magnitude of diffusion coefficient in relation to oceanographic conditions: (salinity, dissolved organic matter concentration). This goal will be achieved through qualitative and quantitative characterization of the dissolved organic matter – DOM in the Baltic Sea deep’s bottom sediments pore waters and overlaying near bottom water and water column in different oceanographic conditions with use of absorption and fluorescence spectroscopy and High Performance Size-Exclusion Chromatography and established correlation between optical characteristics of DOM and concentration of dissolved iron and dissolved organic carbon. Comparison of DOM composition in sediments pore water, near bottom waters and in overlying water column will enable understanding of DOM transformation processes during its early diagenesis. This project will be executed through the field and laboratory work campaigns undertaken by team of experienced researchers during research cruises on board of r/v Oceania to Bornholm Deep, Gdansk Deep and Gotland Deep in the Baltic Sea. Chosen study sites differ from each other by frequency of bottom ventilation events and there are different physical and chemical water masses characterization (salinity, temperature and dissolved oxygen concentration). Water samples extracted through centrifugation from different types of bottom sediments, from to 5 – cm sediments layer, and from near bottom waters as well as water column will be collected for laboratory spectroscopy and chromatographic analysis and determination of dissolved organic carbon and dissolved iron. There will be simultaneous instrumental in situ measurements of physical and chemical characteristics of water column above sediments coring sites: vertical profiles of salinity, temperature, dissolved oxygen concertation, pH and inherent optical properties including in situ DOM fluorescence will be measured. Collected water and sediments samples will be analyzed in land based laboratory. The absorption and fluorescence spectroscopy analysis, as well as chemical analysis will be done in the laboratory of Marine Physics Department, Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland. Chromatographic analysis will be performed at the laboratory of Danish Technical University, National Institute of Aquatic Resources, DTU Aqua, w Lyngby, Denmark. Spectroscopic analysis will include measurements of absorption spectra by chromophoric dissolved organic matter - CDOM, and measurements of DOM fluorescence excitation emission matrix spectra – EEMs. Chromatographic analysis will enable separation of different molecular weight DOM fractions, and fractionated will undergo spectroscopic analysis. Based on measured CDOM absorption spectra a set of spectral indices related with qualitative DOM properties will be calculated e.g. SUVA254 - a spectral index that is correlated with DOM aromaticity. Measured EEMs matrices will be analyzed with use of multivariate statistics methods. The parallel factor model – PARAFAC – will be developed to identify the dominant DOM fractions e.g. humic acids based on spectral characteristics of derived EEMs components. The fluorescence spectral indices will be calculated based on modeled EEMs spectra. Spectroscopic, chromatographic and environmental measurements results will be analyzed statistically to identify which molecular weight and qualitative DOM fractions is correlated with dissolved iron and dissolved organic carbon. Developed statistical relationships enable to identify DOM fraction which would be most susceptible to migrate and in which direction across sediments/near bottom water interface and be used for approximation of DOM diffusion coefficient. Baltic Sea deeps creates sedimentation basins where heavy metals and Persistent Organic Pollutants accumulates in bottom sediments. Known DOM ability to bound into organic-metallic complexes with heavy metals, will create a possible mechanism of heavy metals and pollutants re-mobilization. The return DOM flux from sediments to near bottom water may transport pollutants from sediments to water column. Determination of DOM diffusion coefficient, and determination of environmental conditions when such flux would occur, could be used as a potential tool for risk assessment for heavy metals and pollutants re-mobilization

Increase of temperatures and loss of sea ice has have dramatically changed the Arctic’s physical system. One of the key factors driving the loss of sea-ice is the ice-albedo feedback resulting in more solar energy accumulated into the surface ocean. Colored dissolved organic matter (CDOM) is a key factor affecting the vertical entrapment of heat and light availability for primary production in the Arctic Ocean. Recent studies in the western Arctic have shown that CDOM can result in over 30% more solar heat entrapment in the surface ocean compared to other open-ocean regions, contributing significantly to accelerated sea-ice melt. Very little is known about the distribution, sources and transformations and feedbacks related to increased CDOM concentrations in the European Arctic. In this project we propose to carry out an extensive study to understand the composition and sources of CDOM and the role of CDOM (and other optically active substances) in the fate of solar energy in the Nordic Seas and European Arctic, and how it contributes to the solar heating of the upper ocean and contributes to sea-ice melt, penetration of harmful ultraviolet (UV) light and light availability (UV and PAR) for primary production. By combining forces from groups with complementing experience and expertise in geochemical tracers, physical oceanography, marine optics and sea-ice geophysics, in Arctic and sub-Arctic seas, and provided the access to the Arctic, and state-of-the-art instrumentation (both in the lab and field) we are set to meet this challenging task. Expected results shall provide new information needed to understand on forcing and feedback mechanisms related with optical and chemical properties of CDOM on radiation budget, heat accumulation and carbon cycle in Nordic Seas and European Arctic sector. Results will provide baseline for sensitivity studies in climatic models testing different scenarios in changes of CDOM concentrations.