Quantification and characterisation of the aerobic degradation of organic-walled dinoflagellate cysts
Final Report Abstract
To obtain better insight into the process of species selective aerobic degradation of organic-walled dinoflagellate cysts in relationship to changes in sedimentary redox conditions and (past) bottom-water oxygen concentrations we (1) quantified the degradation rate of individual dinoflagellate cyst species in oxic and anoxic conditions, (2) documented that degradation rate of dinoflagellate cysts is dependent on ambient oxygen concentration, (3) intended to determine the aerobic degradation of dinoflagellate cysts has a biologic (microbial) or chemical character and (4) tested to what extend the degradation rate of dinoflagellate cysts is influenced by the degradation of other organic components of the ambient sediments. Furthermore, we investigated to what extend the sedimentary dinoflagellate cyst association is influenced by lateral transport in the water column during the settling process. For this we executed 4 research studies that consisted of a degradation experiment executed under controlled natural settings, a field-process study and two downcore studies in natural sedimentary settings. The first study described the results of a five-year degradation experiment carried out in natural settings. For this sediment material with a known dinoflagellate cyst association was exposed to four different ambient oxygen concentrations at two locations in the Ostsee and equatorial Atlantic Ocean. Changes in cyst association were monitored once a year. This study revealed that the degradation rate of cysts is highly dependent on the ambient water column oxygen concentration with highest degradation rates occurring at the highest oxygen concentrations. It furthermore we showed that at intermediate oxygen concentrations total cyst concentrations decreased rapidly within the first year, increased in the second and third year and decrease and become stable in the fourth and fifth years respectively. This can be explained by the loss of components that degrade faster than the labile dinoflagellate cysts, and thus effectively increasing the cyst concentrations per gram of sediment in the second and third year of exposure. Apart from this, this study enabled the determination of the species-specific degradation constants of numerous cysts species of which their vulnerability to aerobic degradation was not known previous top this study. This was notably the case for cyst species produced by heterotrophic dinoflagellates. The second study investigated the potential effects on the sedimentary cyst association of the processes of lateral transport of dinoflagellate cysts during their settling as well as the effects of selective degradation during settling and after deposition. These effects were studied during an active upwelling phase off Cape Blanc (NW Africa) in November 2015. This study is the first to document lateral transport of dinoflagellate cysts in nepheloid layers in the water column as well as just above the sea floor. It shows that the character of the lateral transport differs at different depths in the water column and that its extension is likely to be restricted to about 130 km. Furthermore, this study documents that post-depositional degradation of dinoflagellate cysts overprints the effects of lateral transport on the association. A clear effect of post-depositional degradation on the sedimentary dinoflagellate cyst association is also documented in the third study. Here the effect of a downward penetrating oxidation front on the chemical and dinoflagellate cyst composition of turbiditic sediments of the A and F-turbidites of the Madeira Abyssal Plain have been studied. This study is the first to document anaerobic dinoflagellate cyst degradation in the sulphate reducing “nitrogenous” sediment zone leading to an association change. This study also documents the strong effects of aerobic degradation on the dinoflagellate cyst association. It allowed the determination of the species-specific degradation constants of a large amount of species of which previously no or only general information was available about their vulnerability to aerobic degradation. The fourth study builds further upon the results of the third study and documents the effects of anaerobic and aerobic species specific degradation on the establishment of quantitative environmental reconstructions that are being established with the modern analogue technique. This is a technique that is widely used in dinoflagellate cyst based palaeoceanographic, paleo-environmental and paleo-climatic studies. This study shows that anaerobic and aerobic degradation of dinoflagellate cysts leads to opposite anomalies in upper water temperature, salinity and chlorophyll-a reconstructionsAlthough reconstructions of the non-affected part of the turbidite provide reliable reconstructions, the effects of anaerobic degradation leads to a negative anomaly of about 1°C and 0.7 salinity units as well as a strong positive anomaly of chlorophyll-a reconstructions. Aerobic degradation results in a positive anomaly of about 3.5°C and 1.2 salinity units as well as a strong negative excursion of the chlorophyll-a reconstructions. The results of our studies form valuable basic knowledge about the process and effects of species selective anaerobic and aerobic degradation of dinoflagellate cysts. This information is of major importance in (palaeo- ) environmental, -oceanographic and -climatic as well as stratigraphic studies that are currently being carried out in academia, industry and governmental water quality monitoring programs.
Publications
- (2016). Aerobic Degradation of particulate Organic Matter and benthic microbial turnover rates reflecting ocean redox conditions off NW Africa (ADOMIS). Cruise Report Maria S. Merian MSM 48, pp. 65
Karin Zonneveld, Mario Albert, Lorenz Boom, Donner, Barbara, Friederike Ebersbach, Carmen Friese, Daniel Gray, Catarina Guerreiro, Marcus Klann, Bob Koster, Birgit Lübben, Mara Maeke, Fiona Rochholz, Annegret Rüßbult, Lórànd Silye, Jan-Beerend Stuut, Gerard Versteegh, Weichao Wu
(See online at https://doi.org/10.2312/cr_msm48) - (2017). Species-specific sensitivity of dinoflagellate cysts to aerobic degradation: a 5 years natural exposure experiment. Review of Palaeobotany and Palynology 247, 175-187
Gray, D., Zonneveld, K.A.F., Versteegh, G.J.M.
(See online at https://doi.org/10.1016/j.revpalbo.2017.09.002) - (2018): Transport of organic-walled dinoflagellate cysts in nepheloid layers off Cape Blanc (N-W Africa). In: Deep Sea Research Part I: Oceanographic Research Papers 139, S. 55–67
Zonneveld, K.A.F., Ebersbach, F., Maeke, M, Versteegh, G.J.M.
(See online at https://doi.org/10.1016/j.dsr.2018.06.003)
