Quantification and characterisation of the aerobic degradation of organic-walled dinoflagellate cysts

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Organic walled dinoflagellate cysts are taxonomically well defined kerogen particles that show large species specific variation in their vulnerability to early diagenetic aerobic degradation. As representative of organic matter particles with differential lability, this makes them useful to study particulate organic matter degradation processes. As they are used both in industry and in academia as tools to reconstruct palaeoenvironment, palaeoceanography and determine the stratigraphy of marine archives it is essential to gain information about the process of degradation and its controlling factors. In this study we aim to enlarge this information by quantifying the species specific degradation rates in relationship with oxygen concentrations and to determine the biologic (microbial) and/or chemical character of the degradation process. This information can form the basis for a method to quantify past bottom/pore water oxygen concentrations from sedimentary archives. Apart from this we will investigate if cyst degradation is influenced by differences in the amount and composition of organic matter of differential lability in the ambient sedimentary environment. For this we will study the degradation process of the dinoflagellate cysts in a laboratory and field experiments under controlled redox conditions as well as in downcore studies. In the laboratory experiment, sediments with a known cysts composition will be incubated under oxic and anoxic conditions. Material for these experiments is derived from two high productivity regime sites with anoxic bottom waters (eastern Arabian Sea, off NW Africa) and two low productivity regime sites (central eastern Mediterranean discovery basin brine (anoxic) and sediments of the basin margin (oxic). In the field experiment, autoclaved sediments from the Arabian sea oxygen minimum zone with a known cyst composition have been partitioned and transferred to bags composed of dialysis membrane (microbe tight but diffusible for oxygen) and polycarbonate gaze with a pore size of 5 mu-m (penetration of both microbes and oxygen). The material has been exposed to oxic, suboxic and hypoxic natural environments for five years in different water masses of which the oxygen contend is known or monitored. Aliquots of these sediments have been harvested once a year from 2008 to 2013. For determination of the relationship between pore water oxygen concentrations and degradation rates of dinoflagellate cysts in subsurface sediments, the downcore alteration in cyst concentration and association composition in multicore sediments from the Eastern Mediterranean Discovery Basin brine system and the oxygen minimum zones of the Arabian Sea and off NW Africa will be compared to already known oxygen concentrations in pore waters. Furthermore the degradation will be studies along pore water oxygen gradients related to downward and upward moving oxidation fronts in multi and gravity cores of the Discovery Basin region.